It is now standard practice that the Big 4 firms will invite you to a dinner the night before the interviews. Don't be fooled- dinner is an interview. A lot of your time as an associate will include luncheons with clients and they want to make sure you can be comfortable, relaxed, intelligent, and most importantly neat.
My dinner was done as a group of 6 people (3 candidates, 2 associates, 1 partner) at a local restaurant. It was a very nice dinner. Making conversation is important, but it's equally important not to be a conversation bully. Be active but not overbearing.
The next morning started with presentations by several employees of varying levels in audit. PwC did a great job of selling themselves. After the presentations, each candidate was matched up with a "buddy" associate to take us to our interviews. I met with a Sr. Manager and a Partner- some people met with two partners. All interviews are conversational. They hardly ask anything that could be considered behavioral, it was all about having a smooth dialog with someone you just met. My experience was that you should still have several good questions to ask before you get there, but that you may not need them if you can listen to what they tell you about themselves and ask questions based on that.
After the interviews, they took all the candidates to a room to have another meeting on benefits at PwC and then out to lunch. Lunch was also done in groups of 6 (3 candidate- 3 buddys) and it's really casual. Just keep in mind that if you say something especially stupid, they WILL tell the partners and managers, so use your brain.
I got a call from the partner I interviewed with about 3 hours after lunch. I accepted my offer.