If you dig back through this thread you can find my Haas interview writeup which may be helpful even though it was with an alum rather than on-campus with AdCom or a student. My interview was in late December so I think the post was somewhere around then. Even though I had an off-campus interview, the advice I got from a second-year student interviewer was pretty consistent with the general interview prep stuff you see for any school. And it seemed to be on track--I didn't get any curveball questions.
One Haas-specific thing I'd recommend you to be familiar with is the school's list of defining principles...i.e. question the status quo, students always, beyond yourself, confidence without attitude. You should have already covered one of those in your application essays, but my alum interviewer asked me for an example of a time I had questioned the status quo. Based on how big a deal the administration makes about the culture I would expect to get asked about those principles in one form or another during your interview. Following the Dean's tweets (@richlyons) is another good idea, he posts good stuff on a pretty regular basis and it wouldn't hurt to be able to reference something like that during your interview.
Email some students in clubs or career field groups that you're interested in--any random Haas student you contact is likely to be very willing to help you out during your visit, so that aspect of the school's culture would also be something good to talk about during your interview. Being able to mention names is a plus, particularly if you're interviewing with a student who most likely knows your guide since Haas is such a small program. Plus a student will be able to give you a better tour than if you had to self-guide things.
EDIT: This post
calling-all-berkeley-haas-fall-2011-applicants-93931-980.html#p862190