After a few days, I got an email, and while it was very positive on my technical/engineering abilities, ultimately they thought I was "too mature" for the team and might not be a good fit. I was somewhat disappointed, as I liked these guys and thought they had an idea that I could really dig deep into, but I can understand the need to make sure the team is clicking at close to optimal efficiency as possible. I just have never had the "too mature" reason used before. My thoughts at this point are that either:
A) They felt that was an easy way to say they weren't really interested. Strange, but that's ok.
B) They were not happy with the potential for me to leave after a few months. Very legitimate, but there's always some flexibility and we could have talked some more about it and changed plans.
C) I just was too serious during the interview process, and didn't seem like I could work comfortably with the team. I think this is very possible, but usually when interviewing it seems hard to get too comfortable. There's a lot of evaluation going on from both sides, and you want to put your best face forward. For me that usually means trying to look capable and professional.
Anyway, I think they're a great company and will blow up in the next few years, but this just struck me as a strange one, so I thought I would cheer myself up and see if anyone else had any funny or weird stories about interviews.