It was a pretty laid back interview day when I was there. They really emphasize that you should sit in on at least part of a class while you're there so you can get a feel for the place. It was a pretty typical interview day, and you're done pretty early (around 1:30). You might want to check out the interview feedback on SDN for more info.
the least stressful interview i had by far. i wouldn't really worry about anything. maybe, bring a book or homework or something because you may have some downtown while you're waiting for everyone to gather for the tour.