I just had my interview today! They pass around this basket of questions that was the same as the ones listed on SDN for the interview feedback. You have to do two for the group. As for PBL, I don't think it was all that difficult. Just pay attention when they talk about the process in the first part of the day. I forget the specific names, but there are 3 steps to the process and just know how to do each one. I think there is a paper about it in the dropbox but it's super complicated. I found it really easy during the interview, but it may be difficult to let your voice be heard if there are dominating people in the room, so speak up! But don't be too dominant. I really don't see how you could prepare beforehand, but I didn't personally find it stressful or intimidating at all. Maybe I just had a good interview group that worked well together.