At All Things Digital World Headquarters*, our huge staff of expert analysts** is always keeping track of two things: The latest trends in tech and media, and the latest jargon used to hype those trends.

This year, as we convene the seventh edition of D: All Things Digital, we think something major is happening at the intersection of tech and media, and we think it deserves its own new hyped-up name: Web 3.0. Yes, folks, we are declaring the Web 2.0 era over, because, well, when you run conferences and Web sites, you can say stuff like that.

But, if you read on a bit, you will see that we actually have some real, rational basis for believing that yet another seminal moment has arrived in the never-ending digital revolution that inspired us to launch this gathering. And, as you will observe over the next few days, we have assembled what we think is a stellar lineup of speakers to address this major change and other topics.

First, though, a few words about the elephant in the ballroom: The Great Recession. Or, as we like to call it on the AllThingsD.com Web site: The Econalypse. We started work on launching D during the last tech bust, and we believed then that — despite the very real economic woes afflicting the industry–the digital tidal wave sweeping the world wasn’t stopping. In fact, it was during that last recession that the iPod, iTunes, Windows XP, Mac OS X and early social networking services, like Friendster and LinkedIn, were born.

We are painfully aware that this crisis is far worse–we work at a media company, after all, and media companies have been economic piñatas lately. We do not in any way underestimate the economic pain and danger still under way all over the world. But we still believe the digital tidal wave rolls on. And we are immensely grateful to all of you for continuing to attend D under these tough circumstances. In fact, your support has been so strong that we actually sold out a few days earlier this year than last.

So what’s the seminal development that’s ushering in the era of Web 3.0? It’s the real arrival, after years of false predictions, of the thin client, running clean, simple software, against cloud-based data and services. The poster children for this new era have been the Apple iPhone and iPod Touch, which have sold 37 million units in less than two years and attracted 35,000 apps and one billion app downloads in just nine months.

The excitement and energy around the iPhone and the Touch–and the software and services being written for them–remind us of the formative years of the PC and PC software, in the early 1980s, or the early days of the Web in the mid-1990s.

It’s a big deal.

But this is not just about one company, one platform or even one form factor. No, this new phenomenon is about handheld computers from many companies, with software platforms and distribution mechanisms tightly tied to cloud-based services, whether they are multi-player games, e-commerce offerings or corporate databases.

Already Palm, Research in Motion, Nokia, Microsoft and others are hot on Apple’s tail. You will hear from them here at D. And a profusion of new devices, software development kits, app stores and cloud-based services has been announced in the teeth of the economic downturn.

Some of these handheld computers will make phone calls, but others won’t. Some will fit in a pocket, but others will be tablets or even laptop-type clamshells. But, like the iPhone, all will be fusions of clever new hardware, innovative client software and powerful server-based components.

And media companies are on the case, too. You can already read The Wall Street Journal and other news sources, complete with photos and videos, on the iPhone, the BlackBerry and the Kindle, and new handheld devices are coming that are tailored to news. Our own AllThingsD iPhone app will be out by the time you read this. And consumers can stream radio and TV, and even follow live sports events, on pocket devices.

Over the next few days, you’ll hear from Microsoft CEO Steve Ballmer, whose company makes software for both the new platforms and the traditional PCs they threaten. And the leaders of the hottest social network, Twitter, Evan Williams and Biz Stone, will talk about its future. Speaking of the future of social networking, we have invited News Corp. digital head Jon Miller and MySpace CEO Owen Van Natta, who were recently brought in to reinvigorate the media giant’s business, to talk about how they plan to do just that.

You’ll hear from new Yahoo CEO Carol Bartz, who’s trying to deal with rivals and suitors just as the new era is dawning. Also on stage will be the leaders of some key companies making the handheld computers’ hardware and software: Mike Lazaridis of RIM; Jon Rubinstein and Roger McNamee of Palm; and Olli-Pekka Kallasvuo of the worldwide mobile phone leader, Nokia.

From the telecom side, there’ll be Randall Stephenson of AT&T. Cable pioneer and media mogul John Malone will offer his perspective on the future of television.

And, from the content world, we’ll have Jeff Zucker of NBC, Irving Azoff of Ticketmaster, Mark Cuban of HDNet, blogging queen Arianna Huffington and Washington Post publisher Katharine Weymouth.

The leaders of Mozilla, Mitchell Baker and John Lilly, will talk about the role of Web browsers and open source. And playwright Eve Ensler will explain how all this shiny technology is tied, unwittingly, to a crisis thousands of miles away.

So sit back, open your minds, and get ready for Web 3.0.

*Actually, just a cottage in back of Kara’s house.

**Actually, just a handful of journalists, a couple of editors, a geek and an intern, plus some business people.

What I don’t mean to include in this new class of devices are netbooks running Microsoft Windows, which are just fine, but are really merely small, cheap laptops. Nor do I mean to include the tens of millions of older, less capable, phones labeled “smartphones,” which can be a slippery term.

These devices, like the Palm Treo, older Windows Mobile phones, or older-model BlackBerries, were breakthrough products in their day. But they use wimpier operating systems and less capable hardware than today’s new class of smartphones. They do run third-party apps, but these look primitive compared with, say, an iPhone app.

A battle is shaping up in the next few years to see who will dominate this new handheld platform–who will attract the most users and third-party apps?

So, here’s a quick snapshot of the strengths and weaknesses of the main combatants in the war for the handheld platform.

Apple

Strengths: Having defined this new class of handheld computers, Apple has a huge head start, with 30 million modern devices running a powerful and attractive operating system. That includes 17 million iPhones, plus Apple’s secret weapon: 13 million iPod Touches, which do almost all that an iPhone does, except connect to the cellphone networks. Apple (AAPL) also has an easy-to-use app store, which is now estimated to hold over 30,000 apps that have been downloaded over 900 million times in just about nine months. The iPhone also offers wireless synchronization via MobileMe and Microsoft Exchange, and has had terrific marketing. And rumors persist that Apple is working on a cheaper iPhone, and/or a larger iPod Touch, in a tablet format.

Weaknesses: Apple has three key vulnerabilities. First, there are millions of people who prefer a physical keyboard, which the iPhone and Touch lack. Second, at least in the U.S., the iPhone is tied to a single carrier, AT&T (T), whose 3G network is still lousy in some major areas. Finally, while the iPhone’s $199 price has been good enough to make it a hit, people in a deep recession might respond better to a lower price, even if it was for a stripped-down lesser model.

Research in Motion

Strengths: The BlackBerry is an icon, beloved by many, with a large installed base estimated at over 50 million. The company has made progress in migrating the BlackBerry to consumers from corporate IT departments. It understands the importance of software, and has launched its own Apple-like app store, with a decent initial selection. It has a robust marketing campaign and is available from multiple carriers. Most models have physical keyboards.

Weaknesses: The new BlackBerry app platform leaves out much of the installed base; it only works on BlackBerry models introduced after the fall of 2006. RIM (RIMM) stumbled with its first touchscreen BlackBerry, the Storm. And its app store, and the apps themselves in many cases, are clumsier and less polished than the iPhone’s. Most of all, the BlackBerry desperately needs a major user-interface overhaul. Email addicts who know lots of shortcuts love the UI, but it’s very dated for a world where the device must do more than email. There are way too many clicks, steps and menus, and the browser is still weak. RIM has just hired a new user interface guru who worked at Apple and Microsoft, so it apparently gets this problem.

Microsoft

Strengths: Windows Mobile has a large installed base, with many developers who created lots of apps for older versions of the software platform. Microsoft (MSFT) also plans an app store. The company has also launched a wireless synchronization service for consumers, called My Phone. Unlike Apple or RIM, Microsoft has a horizontal strategy, which places its platform on the hardware of numerous handset makers and carriers. The operating system can work with or without a physical keyboard.

Weaknesses: Windows Mobile is old. It is less powerful than the iPhone OS or Android, and has a user interface that needs a major redo. The company laughed off the iPhone phenomenon, and is now late in catching up. A minor new release is planned for this year, but Microsoft is racing to do a complete overhaul of Windows Mobile, called version 7. Unfortunately, that won’t be out till 2010. The new app store won’t work with current versions of Windows Mobile.

And, currently, Windows Mobile lacks a killer hardware device. The best Windows Mobile phones today are models from HTC that feature HTC’s own software, which works to hide as much of the hidebound Windows Mobile user interface as possible. It isn’t clear that apps built for the HTC user interface will work properly on regular Windows Mobile phones, and vice versa.

Google

Strengths: Android is modern and powerful–different from, but in the same class with, the iPhone OS. It has an app store, and excellent wireless synchronization with Google’s calendar and contacts. Like Windows Mobile, it’s a horizontal product, which can be used on numerous handsets and even tablets or netbooks, some of which are rumored to be in the works. It will be available on multiple carriers, and can work with or without a physical keyboard.

Weaknesses: The first Android phone, the T-Mobile G1, was clunky and didn’t set the world on fire. The Android app store has so far attracted surprisingly few apps compared to Apple’s at the same stage. Some users might balk at the tight tie-in with Google (GOOG). Handset makers can build Android phones that aren’t tied in to Google services, so it will be important to see how these variants fare. Another problem is that, as versions of Android diverge among handset makers and carriers, app developers may face a compatibility challenge.

Palm

Strengths: With a slug of venture capital money, and the leadership of an ex-Apple exec, Palm has reinvented both its software and hardware, after allowing them to grow stale. The new Palm Pre and its new webOS, which will launch this spring, have impressed those who’ve seen them, and appear to have a real shot at competing with the iPhone and BlackBerry. The new platform is built for wireless synchronization and third-party developers, and, unlike the iPhone, and some planned Android models, the Pre combines its touchscreen features with a  physical keyboard.

Weaknesses: Even if the phone and OS are hailed once reviewers test them, there are many business issues for Palm (PALM). The company is running on fumes, financially, and its launch carrier, Sprint (S), is hemorrhaging as well. That could make it tough to subsidize the Pre enough to compete on price with the iPhone and BlackBerry, especially if Apple does a cheaper iPhone. In addition, Palm will have to mount a costly marketing campaign to match the advertising machines of Apple, RIM and Microsoft. And it may need financial incentives to tempt developers to write apps for the Pre.

Nokia

Strengths: Nokia is the world-wide leader in cellphones, including smartphones (by the loose definition of that term.) It understands that software and cloud services are key, and has launched an online service called Ovi. There are many older apps already for the Symbian operating system that powers most Nokia models, and Nokia (NOK) is working on an app store. The company is good at hardware, and has huge brand loyalty, at least outside the U.S. And its best known smartphones have physical keyboards.

Weaknesses: Nokia’s software has been inferior to Apple’s and Google’s. To fix this, the company has handed off Symbian to an open-source consortium with a complicated structure. That could make Symbian, and thus Nokia, less nimble than Apple, RIM or Google. Some of Nokia’s competitors will also be using this new Symbian, attempting to differentiate their products with user interface and feature differences. Thus as in the case of Android, there’s a danger that, if variations of Symbian diverge too much, application compatibility could become  a problem. The company also has historically been only a minor player in the very important U.S. market.