Of the several mobile friend-finder apps launching or updating at South by Southwest, Domo has perhaps the most engaging yet inexplicable demo. Two weeks ago at the Launch conference, founder Takahito Iguchi gave a Richard Simmons-like presentation that knocked the crowd flat (video is by VentureBeat). But afterward, few in the crowd could explain what the app actually does.
Here's what it does: It helps you find Facebook people who are near you and share your interests. The mobile app records your interests, musical tastes, work history, and so on, and then lets you find people nearby who match some or all of those categories. If you're at SXSW and want to find someone who shares your interest in a particular musical group, Domo will help you find that person; you can message them through the app as well.
I can see it being useful to connect with friends from work when I'm at big events (the Maker Faire comes to mind). FourSquare will also do this, but FourSquare users have to check in. Domo, I believe, will update your location as long as you have the app running in the background on your phone. (If the app isn't running, and for users who don't have it, it just gets location from Facebook profiles--much less useful.) Domo should also just let you see all users with a public Facebook profile who are nearby. From that list, then, you'll be able to filter to find the people that have compatible interests.
It's actually not a very complex idea, but it is socially powerful. Domo's implementation appears technically adept, even if its user interface is a bit overwrought. As I said, there are other apps launching soon that push social serendipity. It's going to be a big trend at SXSW and likely for the rest of this year.