Last year, rival cellphone manufacturers used the event to announce their own touchscreen smartphones.

This year, what’s getting the love is the iTunes App Store, with its 20,000-plus applications and half a billion downloads.

Among the announcements making headlines this week:

• Nokia’s Ovi Store. An online app and media portal that comes “pre-integrated” on Nokia’s (NOK) new N97 (right), but will be available for download on a slew of existing Nokia phones come May. (link)
• Windows Marketplace. Along with a new version of Windows Mobile, Microsoft (MSFT) announced Monday that it will open a new Windows Marketplace offering — you guessed it — 20,000 apps, some of which actually run on mobile devices. (link)
• App Store for Symbian. PocketGear, which had previously built its own Palm App Store and an App Store for Windows Mobile, unveiled an App Store for Symbian, the operating system that runs Nokia’s smartphones. How it will compete with the Ovi Store remains to be seen.
• Android Market. Google (GOOG) opened an application marketplace for the Android platform last October, but so far it has only accepted free apps. Look for an announcement from Google this week about how that’s going to change.
• BlackBerry Applications Center. Research in Motion (RIMM) invited developers to submit programs to its forthcoming Applications Center in October. We may be hearing more this week about when that will open for business.
• Palm Software Store. This one went live in December with 2,000 apps and 1,000 free games available for download to both Palm (PALM) OS devices and Windows Mobile.

Also making news in Barcelona is Adobe (ADBE), which announced Sunday that it expects to ship a full-fledged version of its Flash player in 2010 that will run on Windows Mobile, Google’s Android, Nokia’s Symbian and the new Palm OS. Steve Jobs had complained that Flash Lite wasn’t good enough for his iPhone. Last we heard, Adobe and Apple were working together to get Flash up to speed, but apparently they’re not there yet.

“We would love to see it on the iPhone, too,” said Adobe’s Anup Murarka, according to a report on CNET.com. “But it’s Apple’s decision on when and how they support any new technology. So we will continue to work on it.” (link)

For comprehensive — if somewhat breathless — coverage of Mobile World Congress 2009, check out Engadget here.

UPDATE: We weren’t kidding about Barcelona’s pickpockets. On Thursday, the London Telegraph reported that Microsoft execs were “in a panic” after a cellphone loaded with a top-secret copy of Windows Media 6.5 was lifted from the pocket of an Australian telecommunications executive. See here.