FWIW, if anyone cares, I think the interview went well. I wore a sportcoat but no tie. The jacket only lasted about one block out of the metro station. It was just too hot. The security guard even showed me the mensroom to "dry off" if I wanted.
I definitely needed it.
My talk seemed to go well and they really seemed to be selling the job to me more than grilling me about my qualifications. They all have been there a long time too which says a lot about how much they like it and also about the job security. And the work looks really cool (if you're an econ dork like me).