http://www.meetup.com/TechBreakfast/
Edit: I just realized that the link points to the same meetup group -- not sure if they're run/organized by the same folks or not.
HacDC http://www.meetup.com/hac-dc/
NOVA Makers http://www.meetup.com/NOVA-Makers/
I haven't been to either, but have been meaning to get to one of the NOVA makers happy hours for a while.
I'm in VA (Fairfax) and would be interested to participate probably not tomorrow as I'm busy. But I honestly don't feel like driving just for happy hour, I'm very social but I'd rather come and discuss/discover a topic. I'll be happy to present something around security (I work in security research in different DARPA project). I believe this would create connection based on technical interest rather than social affinity.
I wonder when Meetup is going to start suggesting events based on the people who are going. I can imagine they have a massive amount of data, with a huge graph of connections behind it. I can recall when joining it sucked about 98,000 parameters from my Facebook profile into it.
It's trivial to show me things I might enjoy based on a few tags, like, "oh you like ruby so you might like this hackathon on friday" I'd love it if they put that data they've got on me to use, however, and started to suggest things like "hey it looks like you and about 15 people attending this nuclear fusion discussion would really get along, want to learn more??"
I think the value of meetup's in general is the people that go and the social interaction, not necessarily the topic at hand. I'd even go to a web programming with QBASIC meetup (get it, goto, haha) if I knew that there were some cool people there that I might want to talk to.
On second thought, a QBASIC web programming meetup would be a good time no matter what.