I'm amazed how many sites completely disregard the international audience.
I'd put something like:
"Hackathonia is a great way to find "Hackathons" near you. Hackathons bring bright, motivated people together to build amazing apps in competitive yet collaborative, team-based competitions."
That way you get to the meat of what you do faster.
Don't make me create yet another online account. Just about every hacker will have an OpenID, Twitter, FB, or Google account.
Use square avatars. I can't imagine all that many people have 160x190px images hanging around. Also use http://en.gravatar.com/ as a default.
Include a more link in the "tweets tagged" box. Maybe to Google's realtime search: http://www.google.com/search?q=%23SDCChi&tbo=1&tbs=r...
What's the radius you've set for your search? I put in an East Bay zip (in the SF Bay Area) and nothing came up.