This is definitely a big loss for Austin. There are still a few interesting startups in the area, but Gowalla was the one that made it a serious contender.
In terms of other startups, we have Other Inbox, Infochimps, WPEngine, and a number of other things that are relatively quiet. In terms of "big" players, we have Facebook, Evernote, Zynga, some of Sony's game dev (DC Universe Online started here), and Ebay/Paypal is moving in. OpsCode and Mozilla both have lead evangelists here too.
And there are probably dozens of things I'm missing..
Disclosure: I'm a Developer Evangelist for Twilio and based in Austin.
Outside of the startup world: Apple, IBM, Dell and AMD have major campuses in Austin.
I grew up in Austin and live in NYC. I love seeing Austin companies make waves, but I feel like the startup scene there is still in its early stages.
Gowalla isn't involved in the community.