Northern Virginia for any sort of federal work, though it's not the same situation since the clearance requirements disqualify most non-citizens, people of foreign birth, or just most people at all since most people don't have security clearances. Still fertile ground for people who meet the requirements, though.
Agreed. I think defense startups are different animals though, based on my experience as a contractor in startup size defense contracting firms in the past. I could see different networking circles, different hiring requirements (you mentioned clearances), different software setups (I've worked on teams where using git over ssh not allowed on government networks). I plan the curate the results from this ask into https://github.com/BillBarnhill/AwesomeStartupHubs, and will include defense hubs there too.
