I attended both the information session and the coffeehouse chats that Bain held on-campus prior to my interview with them. In my experience, you can tell a lot about the priorities of a company with regards to how they feel about their human capital through their interview process. That said, Bain has NO behavioral interview for its first round. It consists of two separate case interviews with two different interviewers (senior managers or partners). Practice your cases with friends, by yourself, with your significant other, and anyone else you can wrangle before you step into the interview room. You will NOT advance to the next round on the merits of your looks and charm alone. That said, they do genuinely want you to do well and to not be too nervous. They provide you with a mock interview workshop in their office a few nights before and assign you a resource (who, for me, was very pro-active about reaching out) who is currently an AC and usually a relatively new hire who can give you good advice and empathize.
Unfortunately for me, I was cut down by a bad case of the flu the night before my interview. Moral of the story: don't forget to take care of yourself during recruiting season. Get your rest, wash your hands often, and make sure you get your vitamins.