In a bold and definitive move, AOL is paying $315 million, mostly in cash, to buy the Huffington Post, one of the Web’s most prominent news and opinion sites.

As part of the deal, Huffington Post co-founder Arianna Huffington (pictured here)–who was derided by some when she co-founded the left-leaning site in 2005 with investor and well-known communications exec Kenneth Lerer–will become president and editor in chief of the Huffington Post Media Group within AOL.

The deal was signed late this afternoon, and the board of directors of each company and shareholders of the privately held Huffington Post have approved the transaction.

In an exclusive video interview BoomTown conducted earlier today in Dallas, just before Super Bowl XLV, both Armstrong and Huffington were jovial that the whirlwind deal, begun in November, actually worked out so quickly.

Perhaps giddy, they hit upon a common motto:

“One plus one equals 11.”

Get it? One and one next to each other is the number 11!

Let’s move on, shall we?

AOL said it is expected to close in the late-first or early-second quarter of 2011.

Once culminated, it will put Huffington in charge of all AOL content and other properties, including well-known names such as Engadget, Moviefone, MapQuest and TechCrunch.

She said she plans to move to New York from Los Angeles, although she will also maintain her longtime Brentwood home there.

And content for all these sites will be integrated deeply into the Huffington Post, giving it a huge new infusion of editorial material.

More to the point, the flashy acquisition–which essentially came together in less than two weeks in January–will become the linchpin of AOL CEO Tim Armstrong’s aggressive, if risky, strategy to focus the long-troubled company as a content and advertising powerhouse.

For AOL, the deal gives it a popular branded site that is very good at generating lots of page views and impressions very efficiently–which is the company’s whole thrust these days.

That means lots more ad inventory to sell and an injection of content talent, giving AOL the scale it desperately needs.

The move also obviously gives AOL a much-needed editorial identity and cohesion, which it doesn’t really have.

In fact, many think AOL needs a rallying point to bring clarity to its hodgepodge of recent acquisitions that all center on the notion that a strong company has yet to emerge in the premium content space.

Here is a mock-up of the front page of AOL tonight (click on it to make it larger):

While it all makes for a riveting narrative by the charming Armstrong, AOL still has not delivered the business turnaround promised after its spinoff from Time Warner in 2009.

Wall Street, which has given Armstrong a lot of rope, has become more impatient of late to see results–especially more robust increases in its display advertising business, as its access business dies off–after AOL spun off from Time Warner in 2009.

In its quarterly report last week, AOL reported earnings of 61 cents a share on revenue of $596 million.

But, as MediaMemo’s Peter Kafka wrote:

The bigger picture is that Armstrong’s turnaround is still in progress. Ad revenue was down 29 percent in the last quarter, although that number is worse than it looks. A big chunk of the decline comes from moves AOL has intentionally made that will cut revenue in the short run in return for more profitable sales down the road.

A more representative data set for Armstrong are his display ad sales, which are down 14 percent overall and eight percent in the U.S..

The bad news is that the rest of the Web ad industry is well into rebound mode; the good news is that AOL has trained Wall Street to expect numbers like these. If you’re waiting to see positive sales numbers, Armstrong said during AOL’s earnings call this morning, wait until the second half of this year.

In any case, the move is a good one for the Huffington Post since it will vault it to the next level of growth.

Other companies, such as Yahoo and NBC Universal, had looked at the company as a purchase target, and many expected it to eventually sell out to a larger company.

Sources close to the Huffington Post said that that outcome seemed the most likely, and the recent expansion of the site and its audience made it a good time to do a deal now.

Talks with Yahoo last year went nowhere, sources said, but Armstrong was not as slow to act.

Indeed, the actual deal happened quickly, said Armstrong and Huffington in a video interview with BoomTown earlier today (which you can see here).

The pair started talking in early November of last year at the Quadrangle Conference in New York and continued their discussions through the holidays.

Armstrong made the official offer to Huffington by phone in January, while she was at the World Economic Forum in Davos, Switzerland, and he was snowed in in New York.

Five time multiple to the Huffington Post’s upward of $60 million in expected revenue for the coming year, and nearly 10 times the $31 million for 2010, the offer was accepted quickly.

AOL used cash for $300 million of the purchase and $15 million in stock for the rest.

“The idea of turning a fire hose of traffic onto our content made enormous sense,” said one person close to the situation. “Everything is changing so fast, it seemed like the time was right.”

An IPO was also considered for the Huffington Post, sources said. But since the site only recently moved into profitability–although barely–such an event would have been farther out.

That’s despite the fact that the Huffington Post has seen fast-growing traffic and influence, spurred in part by Huffington’s larger-than-life persona in both the mainstream media and blogosphere.

The wide-ranging site–which has added a number of content areas in recent years beyond its flagship political offering–currently has almost 26 million unique monthly visitors, according to recent stats, moving in close range to established news organizations such as the New York Times.

That kind of success seemed unlikely when the Huffington Post launched on May 9, 2005, positioning itself as as a liberal counterweight to the popular right-leaning Drudge Report.

But the Huffington Post’s heady mix of celebrity bloggers, personality and voice, as well as aggressive curation of links from other sites, quickly caught on.

To fund its efforts, the New York-based online media company has raised $37 million from angel investors such as Lerer–the largest individual shareholder, followed closely by Huffington–and venture firms such as Greycroft Partners, Softbank Capital and Oak Investment Partners.

The growth has not been without controversy around issues such as lack of payments to bloggers who contribute and accusations that the site uses too much content from other Web sources when linking.

And Huffington herself has also been a lightning rod, which has been both positive and negative for the site.

But, there is no question she is one of the Web’s most prominent players, along with writing books, appearing on television frequently and being a fixture at high-profile events in New York, Los Angeles and Washington, D.C.

That includes a never-ending panoply of parties that feature a potent mix of movie stars, corporate poo-bahs, glad-handing politicians and lots of journalists from all over the media.

In fact, full disclosure, I was at one of those parties this past weekend for actor Colin Firth and others involved in the making of the Oscar-nominated film “The King’s Speech.” (Apropos of nothing, actor Helena Bonham Carter is as smart as you would expect, but much more delicate.)

As part of the AOL deal, CEO Eric Hippeau–who has been integral to professionalizing the business and will be joining Lerer Ventures–and Chief Revenue Officer Greg Coleman will leave the Huffington Post.

Ironically, Coleman was replaced by Armstrong as head of ad sales at AOL after he took over as CEO. Coleman got a big payout and will now apparently get another.

But the rest of the 200 Huffington Post employees are moving over to AOL with Huffington, who Armstrong hopes will be the company’s ace in the content hole going forward.

There are likely to be changes to come too at AOL, within weeks, especially in its content-side management and site staffs.

AOL provided some quotes in support of the deal from prominent Internet figures who know Huffington well.

“Arianna is one of the preeminent authors and editors of our time, and Tim has a remarkable track record of business success,” said Facebook COO Sheryl Sandberg. “Bringing them together creates tremendous potential for AOL.”

And Twitter co-founder Biz Stone said:

“Editorial vision and leadership are essential in order to transmute our shared cacophony of voices into a valuable dialogue. Arianna’s expertise, empathy, and entrepreneurial enthusiasm forms a kind of alchemy turning mere words and phrases into powerful expressions of humanity.”

Inter-Internet harmony: How sweet!

Here is the official press release, with all the details, but there is also an 8 am ET AOL conference call tomorrow:

AOL AGREES TO ACQUIRE THE HUFFINGTON POST

Acquisition Will Solidify AOL’s Strategy of Creating a Premier Content Network With Local, National and International Reach

Arianna Huffington To Lead Newly Formed The Huffington Post Media Group Which Will Integrate All Huffington Post and AOL Content, Including News, Tech, Women, Local, Multicultural, Entertainment, Video, Community, and More

The New Combined Media Group Will Reach 117 Million Americans and 270 Million Globally

Group Uniquely Positioned To Redefine the Future of Brand Advertising and Marketing For an Engaged and Influential Audience

New York, NY–February 7, 2011–AOL Inc. [NYSE:AOL] announced today that it has entered into a definitive agreement to acquire The Huffington Post, the influential and rapidly growing news, analysis, and lifestyle website founded in 2005, which now counts nearly 25 million unique monthly visitors*.

The transaction will create a premier global, national, local, and hyper-local content group for the digital age–leveraged across online, mobile, tablet, and video platforms. The combination of AOL’s infrastructure and scale with The Huffington Post’s pioneering approach to news and innovative community building among a broad and sophisticated audience will mark a seminal moment in the evolution of digital journalism and online engagement.

The new group will have a combined base of 117 million unique visitors a month in the United States and 270 million around the world**. Following the close of this transaction, AOL will accelerate its strategy to deliver a scaled and differentiated array of premium news, analysis, and entertainment produced by thousands of writers, editors, reporters, and videographers around the globe.

As part of the transaction, Arianna Huffington, The Huffington Post’s co-founder and editor-in-chief, will be named president and editor-in-chief of The Huffington Post Media Group, which will include all Huffington Post and AOL content, including Engadget, TechCrunch, Moviefone, MapQuest, Black Voices, PopEater, AOL Music, AOL Latino, AutoBlog, Patch, StyleList, and more.

“The acquisition of The Huffington Post will create a next-generation American media company with global reach that combines content, community, and social experiences for consumers,” said Tim Armstrong, Chairman and CEO of AOL. “Together, our companies will embrace the digital future and become a digital destination that delivers unmatched experiences for both consumers and advertisers.”

Armstrong continued, “Arianna is a singularly passionate and dedicated champion of innovative journalistic engagement, and a master of the art of using new media to illuminate, entertain and enhance the national conversation. Arianna is a remarkable person and she will continue to create remarkable outcomes for the combined company.”

“This is truly a merger of visions and a perfect fit for us,” said Huffington. “The Huffington Post will continue on the same path we have been on for the last six years–though now at light speed–by combining with AOL. Our readers will still be able to come to the Huffington Post at the same URL, and find all the same content they’ve grown to love, plus a lot more–more local, more tech, more entertainment, more finance, and lots more video. We are fusing a legendary and powerful new media brand with a vibrant, innovative news organization, known for its distinctive voice, a highly engaged audience, an expertise in community-building, and a track record for demystifying the news and putting flesh and blood on the data while drawing our audience into the conversation.”

Huffington continued, “By uniting AOL and The Huffington Post, we are creating one of the largest destinations for smart content and community on the Internet. And we intend to keep making it better and better.”

Kenneth Lerer, The Huffington Post’s Co-Founder and Chairman, said, “The Huffington Post team has created a potent brand with the proven track record of knowing how to grow traffic, inform and entertain its readers and build a one-of-a-kind online community. Add that to the powerful scale and resources of AOL and you have the perfect combination for today and the future. Together these two companies will be a premier online content provider. From local citizen reporting through AOL’s Patch, to The Huffington Post’s national reporting on politics, business and culture, consumers will have access to everything they want whenever they want it.”

AOL has agreed to purchase The Huffington Post for $315 million, approximately $300 million of which will be paid in cash funded from cash on hand. The Huffington Post is privately owned by its two cofounders, as well as a group of investors. The proposed transaction is subject to customary closing conditions, including receipt of government approvals. The boards of directors of each company and shareholders of The Huffington Post have approved the transaction. The transaction is expected to close in the late first- or early second-quarter 2011.

The Huffington Post over-indexes on educated, affluent users, reaching the key decision makers in C-suites around the globe. The Huffington Post speaks to this influential audience via a host of prominent voices on its group blog. Among those who have blogged on The Huffington Post are: President Barack Obama, Secretary of State Hillary Clinton, Mayor Michael Bloomberg, Larry Page, Diane Sawyer, Buzz Aldrin, Nora Ephron, Bill Maher, Madeleine Albright, Robert Redford, Katie Couric, Neil Young, Rahm Emanuel, Mia Farrow, Senator Russ Feingold, Senator Al Franken, Ari Emanuel, Harry Shearer, Senator John Kerry, Representative Nancy Pelosi, Madonna, Lawrence Summers, Jamie Lee Curtis, Ryan Reynolds, Craig Newmark, Alec Baldwin, Aaron Sorkin, Natalie Portman, Scarlett Johansson, Russell Simmons, Sean Penn, Bill Gates, Norman Lear, Charlie Rose, Elizabeth Warren, Tavis Smiley, Sheryl Sandberg, George Clooney, and former President Bill Clinton. And the audience speaks back, generating four million comments a month***.

The Huffington Post’s affluent, influential audience, that is growing at a rate of 22 percent (December 2009 vs. December 2010)****, when combined with AOL’s massive scale, video offerings and local expertise, will represent an incredibly desirable demographic for a broad range of advertising partners across the board.

And here is Armstrong’s internal memo to the AOL staff:

AOLers,

We are taking another major step in the comeback of AOL. Today we are announcing that we have agreed to acquire The Huffington Post, one of the most exciting, influential, and fastest growing properties on the Internet. We believe in brands, quality journalism, and the positive role of communities in the world–The Huffington Post shares our values and the combination of the two companies will create the premier global and local media company on the Internet.

Co-founded six years ago by Arianna Huffington and Ken Lerer, The Huffington Post has grown to become an industry leader–one of the Web’s most popular and innovative sources of online news, commentary, and information. Arianna and team have created a brand and a destination that focuses on the consumer experience. By combining The Huffington Post with AOL’s network of sites, thriving video offerings, local expertise and enormous reach, we will create a company that is laser-focused on serving our audiences across every platform imaginable–social, local, video, mobile and tablet.

The Huffington Post is core to our strategy and our 80:80:80 focus–80% of domestic spending is done by women, 80% of commerce happens locally and 80% of considered purchases are driven by influencers. The influencer part of the strategy is important and will be potent.

The Huffington Post is a strong influencer brand and it attracts a valuable audience, including a great focus on women’s content. In addition, Arianna Huffington is a world-renowned expert on women’s topics and issues, and has enabled The Huffington Post to grow rapidly by continually developing new audiences.

In the local area, the combination of the two companies will create a scaled connection between global and local communities on one platform. This will create a new way for people to get local and global information in a timely and entertaining way.

The Huffington Post will join the family of AOL Brands that are destinations for an influencer audience, brands like TechCrunch, Engadget, AutoBlog, and Moviefone. Uniquely, The Huffington Post is the platform for influential people–the people that drive trends, commerce, politics, entertainment, news, and information. Adding this strategic platform to our already strong network of sites, including the AOL homepage, has the potential to make AOL the most influential company in the content space.

Arianna Huffington is one of the most successful entrepreneurs in the Internet space and someone that is even more successful in building communities and relationships in every corner of the globe. The Huffington Post and Arianna have created a company that has partnered with the most successful and well-known leaders in all aspects of society that touch important topics to give consumers direct access to the most influential decision makers and community leaders.

This acquisition will create a high-quality and diverse digital ecosystem encompassing local, national and international news, politics, entertainment, technology, fashion, sports, health, personal finance, green, lifestyle, the arts and more. This deal will combine the amazing talent at AOL with the innovative and talented staff of The Huffington Post. Here are just a few high-level points around what this deal brings to market:

* Together, AOL and The Huffington Post will have 117MM unduplicated domestic monthly UVs, and ~270MM monthly UVs worldwide (according to comScore Dec 2010).

* The Huffington Post is one of the fastest growing web properties on the Internet. It grew 22% last year–that’s faster than Twitter, which grew 18% – and 15x as quickly as the Internet grew last year (comScore Dec ’09-’10).

* Both AOL and The Huffington Post count powerful, affluent users among their top loyal visitors, significantly over-indexing in $100K+ income users.

* AOL passed Hulu in unique viewers on video in the fourth quarter of 2010; video views on AOL are up 400 percent year-over-year.

* Between AOL’s innovative Project Devil ad unit, engaging users for 27 seconds longer than traditional display ads, and The Huffington Post’s highly-vocal community, with 4MM+ comments per month, we will marry attention-grabbing content and brand experiences for both advertisers and consumers.

In the local area, the combination of the two companies will create a premier global/local syndication network at scale. This will create a new way for people to get local and global information in a timely, informative and entertaining way.

To maximize the strategic advantage of this great deal, we will be creating a new group at AOL called The Huffington Post Media Group. Within this group will be AOL Media, AOL Local & Mapping, AOL Search and our new friends at The Huffington Post. We will continue operating the towns structure, AOL.com and HuffingtonPost.com.

I’m thrilled to announce that Arianna Huffington will join AOL’s executive team as President and Editor in Chief of The Huffington Post Media Group. We have asked Jon Brod to lead the overall operational integration on the AOL side of the combined entities. Jon will lead the local group integration and work closely with David Eun and the teams in AOL Media. We will work quickly with The Huffington Post to create a combined organizational design to coincide with the deal closing. While we wait for the required regulatory reviews to be completed and the transaction to close before implementing the design, we will move very quickly to plan the details of the integration of the two companies. To this end, we will announce the new organizational structure as soon as possible.

In the meantime, we will continue creating great content and products for our consumers within the town structure and stay laser-focused on the aggressive goals we have set for our winter luge. We are on the right track and will continue our weekly operating cadence and town structure to drive successful results against our company goals.

Here’s a special message for all of you we taped to welcome The Huffington Post and Arianna to our AOL Family:

http://today.office.aol.com/company-news/2011/02/aol-agrees-buy-huffington-post

And of course we wanted to welcome Arianna to our “You’ve Got” video of the day–check her out on AOL.com.

We will be holding a company all hands meeting to address your questions related to today’s exciting news. We will video conference from our New York office on the 6th Floor at 9:30 AM ET and will be joined by Arianna Huffington and key executives from her organization. We will also be holding a call for our west coast offices at 2:00 PM ET and for our Patch offices at 2:45 PM ET. See below for meeting info (conference rooms will be sent out shortly).

AOL is playing to win…and The Huffington Post and AOL will occupy a unique place in the future of the Internet. Let’s go get it done.

–TA

(More full disclosure: As has been previously reported by MediaMemo, All Things Digital had the briefest and most preliminary of discussions with Armstrong about moving to AOL last year, while exploring several other options. All’s well that ended well: We stayed at Dow Jones, which is owned by News Corp.)

While in Los Angeles for a brief second on Friday, BoomTown motored over to the Brentwood home of puckish entrepreneur Jason Calacanis to talk to him about his prank tweets the night before the introduction of the iPad last week.

On Tuesday night before the much hyped launch of the newest device from Apple (AAPL), Calacanis let loose with a series of over-the-top posts to Twitter, claiming he had been a beta tester for the iPad tablet computer for 10 days.

Unfortunately, these were assertions that some in the mostly mainstream media took too seriously.

So was it a jump-the-shark moment for journalism?

It was certainly sloppy, given that Calacanis is well known for slapping Apple around and that the secretive computer giant does not even give its own employees access to new products.

All this might have sent off alarm bells.

But he followed up with a series of tweets on a myriad of features of the new iPad–one nuttier, pricier and heavier than the next, such as a built-in HDTV tuner, a solar recharging pad and more.

For example: “Yes, there are 2cameras: one in front and one in back (or it may be one with some double lens) so you record yourself and in front of u.”

The problem was that a few big media outfits, including CNNMoney.com and WSJ.com, posted reports on the tweets without much of a raised eyebrow or first checking on their veracity with Apple or with Calacanis.

While anyone can get caught in a prank–and this was a pretty elaborate one pulled by Calacanis, who claims he was just trying to point out how ridiculous Apple hype had become–it’s still an instructive moment for journalism.

Here’s my interview with Calacanis, explaining it all (with a little shot of his new baby girl at the end), as well as images of his faux iPad tweets below: