Actually, fairly laid back. The biggest thing is htat they are hard-core acadmic, and if you aren't they don't want you. So if you still want them, leave out your dream to start your own private practice in Alaska.
Have a few "deeper" questions to ask, be prepared to expalin/defend weaknesses in your record, I was asked which programs I would also interview at...otherwise, very standard, the resident are nice. You don't find out with whom you are interviewing until you get to their door. Tour is semiprivate and includes lunch, that was a helpful time. If you are from Harvard, know when anesthesiology was started.
Don't worry about it- you'll want to shine, just like at any place, but a lot of your ranking is going to come off your letters, grades, scores, etc.
the social the night before wa fun, but the food was nachos- messy adn ahrd to eat standing up!-so maybe eat before hand.
hope that helps!
msl