I'll second that. Gowalla was in Austin in name only. Zero presence at any events, no penetration of the startup networks. They moved to Austin from Dallas, I hear, at the behest of investors.
It's interesting how many startups are based here yet Gowalla got the huge press whenever Austin was mentioned. I wonder why this is - is it because of the Foursquare competition initially? Because they launched at SXSW and were a local company?
No clue why they got all the attention.. but @mattt has gotten involved in the community here and there. I've run into him a few times at @damon's Friday Night Hacks.
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.