Just reading the interview feedback section is definitely sufficient. The day is exactly how it is mentioned there; long and informational. It's for you to see if you can see yourself at USC and whether or not you like their PBL curriculum. The mock PBL is nothing to sweat about. Just go in there and be yourself. Talk when need to and allow others to as well. Besides that it is out of your control. The admissions/staff don't interact with you personally so I couldn't see how you can prepare. I know before my interview I read up on PBL, USC's mission and agenda, but in the end it was not needed except to give me more info on USC. Hope that helps. If you need more info you can pm me.