Realtor.com, which is the largest in the highly fragmented market, has launched an iPad application catching up with two of its closest rivals, Trulia and Zillow. Update: The app will actually be live tomorrow.

The top-visited real estate website in March was Realtor.com; however, none of the companies enjoys a commanding lead.  In fact, a new source of traffic for any of them, whether it comes from a mobile phone or tablet, can turn into a first-mover advantage.

Last month, Realtor.com’s market share totaled 6.5 percent, followed by Yahoo! Real Estate and Zillow.com, with 6.04 percent and 5.36 percent respectively. Trulia was listed fourth with 4.63 percent market share, according to Hitwise.

Realtor.com was one of the first online destinations to publish housing listings, and today it is the only one that has a direct relationship with the National Association of REALTORS.

Because of its ties, it gets a direct feed of the information from the Multiple Listing Service and claims to have the most accurate collection of listings because more than 80 percent of all property listings are updated every 15 minutes.

Realtor.com’s parent company, Move Inc., went public in the late ’80s, and last year reported revenues of $197.5 million and a net loss of $20.9 million. Meanwhile, Zillow filed documents with the SEC last week announcing its intentions to go public. In 2010, it’s revenues totaled $30.5 million and it recorded a net loss of $6.8 million. Trulia is also preparing for a public offering.

“Mobile is such an important part of the way you look at real estate now,” said Steve Berkowitz, Move’s CEO. “It’s something we’ve seen grow exponentially year over year.”

The free iPad application is the latest push, joining Realtor.com’s presence on the iPhone, Android and Windows Phone 7. Berkowitz said they don’t break out traffic it receives from mobile devices, but that people are viewing about 10 properties a second from the various apps. So far, mobile traffic does not exceed the PC, but he says the audience is two to three times more engaged than on the Web. Additionally, Realtor.com mobile apps have been downloaded 3.6 million times and active users have increased by 79 percent in the past four months.

With the release of the iPad app, users will be able to use the large screen to search for homes for sale or properties to rent across the country. Users can hunt for homes or open houses based on location, the MLS number, or by city, state, or street name. Listings can be saved to be viewed later, and one feature lets you search a section on the map by circling that area with your fingertip.

As with Realtor.com’s other applications, users can also reach out to an agent to schedule a tour or ask questions. In the past year, Realtor.com mobile apps have contributed to a 240 percent increase in consumer outreach to local agents and in-app communication between agents and consumers has increased by 148 percent since December, Berkowitz said.

Of course, the one downside of the iPad application is that it only works when a user has Wi-Fi connectivity, or if they’ve opted to buy the 3G model.

Realtor.com makes money by charging agents a subscription fee to showcase various listings and make them stand out from the rest. Inclusion in the mobile apps is a part of those rates.

According to numerous sources familiar with Microsoft’s thinking whom I have been talking to this past week, quite a lot–from creating a single search index to forming one common ad platform to running the place with longtime Microsoft execs at the helm.

So let’s just ignore for now the latest wrinkle in this obviously dysfunctional relationship between Yahoo and Microsoft–which is beginning to remind me of that bizarre Charlie Brown, Lucy Van Pelt and football situation.

That’s because once again (and, as it has apparently done over the last year secretly, until Microsoft finally went hostile 10 days ago), Yahoo’s board is expected to deliver another no-thank-you-very-much-for-now in answer to Microsoft’s latest bid–this time a $31-per-share offer.

Fine, fine. We all know this is going to grind forward agonizingly, as investment bankers parry and various scenarios are bandied about (including here in excess, we can assure you!).

And, of course, there will be possible other merger partners leaked. On today’s menu: AOL! Having written two books about the even-more-troubled-than-Yahoo Internet outfit, here is my official response: Yuck.

Thus, to be more helpful, it might be better to focus on some things that might happen if the software giant ever got the keys to Yahoo.

Let’s be clear–nothing has been formally decided by Microsoft brass as yet, but there are some interesting ideas to be found in the planning they did before they prepared the offer, which can give one an outline of their plan if they won.

It’s important to think about, because exactly what Microsoft would do to Yahoo is probably something that Yahoo’s board, executives, employees and others would probably like to get a sense of as it considers what it should do.

First, we already know Microsoft will keep the Yahoo brand name, per public declarations by Microsoft CEO Steve Ballmer. This is kind of a no-brainer, especially when it is compared to the lackluster MSN. (Historical footnote: The code name for MSN was Marvel, which was a much better moniker still!)

Most sources familiar with Microsoft’s thinking could not agree more. One noted that Yahoo was clearly the best brand, but said Microsoft would likely remain “open-minded about what happens to the rest of the MSN-branded names.” Expect Window Live products to have the best chance of survival.

Also on the PowerPoint slides, which Microsoft execs have only vaguely referred to as cost savings, is the consolidation of the search indexes and technology of Yahoo and Microsoft into one product. Signs lean toward Microsoft here, as some of its execs have even publicly insulted Yahoo’s efforts in this arena.

Frankly, neither should be bragging much, given how badly they both lag behind Google, but Microsoft is better equipped from an engineering and power programming point of view to dominate here.

That also goes for the consolidating of the ad platforms, both for search and display. Even though Yahoo dominates the display market, Microsoft considers its recent acquisition of aQuantive to be the driver of this arena, rather than Yahoo’s technology and new purchases like BlueLithium and Right Media.

In both the ad and search efforts, sources said that Microsoft would split engineers between those who work on improving and running the core existing products and another group who will be focused on pushing to incorporate new innovation.

That would include trying to figure out a recent project Yahoo is currently undergoing, which inside sources call a “lugubrious” overhaul of the technology related to its display business. It’s comparable to its ill-fated Panama search-ad fix, a multiyear project Microsoft would probably be inclined to want to make sure is staffed by its own execs.

In that regard, if Microsoft ever prevails, Yahoo better be prepared to meet the parents.

They will be running the Yahoo show and would include Microsoft execs, pictured here, such as:

Brian McAndrews, former aQuantive CEO and now Microsoft’s SVP of its Advertiser Publisher Solutions Group, who is a rising star and would surely play a key role in all ad efforts and coordination.

Satya Nadella, corporate vice president of its Search and Advertising Platform Group, the engineering head whom BoomTown will now dub, “Mr. Search and Destroy,” because he would likely lead all efforts to use Yahoo’s assets to catch Google. (Good luck with that one, Satya!)

Yusuf Mehdi, SVP of Strategic Partnerships, who has been in and out of the MSN businesses many times and is one of Microsoft’s better-known Internet execs outside the company, and who has played an important role in this bid.

And, of course, Kevin Johnson, president of Platforms and Services Division, who runs quite a swath of the company. Besides Ballmer, he is probably the most important player in this effort to turbocharge Microsoft with Yahoo power.

That is, except for Hank Vigil, SVP of Strategy and Partnership, who has worked closely with Ballmer on this deal and also big moves like the recent $240 million Facebook investment. Vigil is not high-profile in any way, but he feels a lot like Zelig in his clearly important presence in a lot of Microsoft’s more bold initiatives.

One major Web exec who will not be part of the hunting party is Steve Berkowitz, SVP of the Online Services Group, who is finally on the way out, as has been long rumored. Sources said his change of status as a major Web player at Microsoft has been communicated to many top execs at the company last week. But it is not clear whether the former Ask.com CEO will leave Microsoft or get another job at the company.

In fact, many a Microsoft Web exec has mysteriously disappeared into the bowels of the company, never to be seen again, so Yahoo execs: Beware!

“We have certainly not bitten an inch out of the hide of Google,” Diller said earlier this week. “I’ve been daunted by the progress of that. … The challenge of the year … is to get people to try [Ask], experiment with it and then adopt it.”

With that in mind, Diller’s making some changes. Ask.com Chief Executive Officer Jim Lanzone–who claimed the CEO spot in April 2006 when Steve Berkowitz took a job at Microsoft–is leaving the company in a management shake-upr that will see former Match.com CEO Jim Safka take his place.

News of the leadership change comes as Ask parent InterActiveCorp prepares to spin off its HSN (Home Shopping Network), Ticketmaster, Interval International and LendingTree properties. “These changes are intended to strengthen and streamline the operating structure at IAC, both leading up to our intended spin-offs, and beyond,” said IAC CEO Diller.

Well, we’ll have to see about that. Certainly, Safka seems like a worthy candidate for the job. As CEO of Match.com from 2004 to 2006, he grew the site’s membership and revenues substantially. That said, Lanzone is also a very smart guy. If he wasn’t able to turn Ask into a legitimate player in the search market, one wonders if anyone can.