We've now run 5 Health 2.0 Developer Challenge Code-a-thons (we have some Federal gov cooperation and they wont let us call then hackathons!). Sure at each one there is chatting and networking but at each one somewhere north of 100 people produce anywhere between 8-12 teams each of whom show what can be built in a short day (9-5). While they're not always fully completed apps, most are, and most have been terrific.
And while it's OK to bring in something that's been worked on before, most of the teams at the code-a-thons meet at the day and integrate medical professionals with coders.
So anyone who wants to come code at an event where what you build might really make a difference (not that we dont love Zunga & FourSquare, but....) check out www.health2challenge.org