Just had my Yale interview!! The interviewer was really nice, outgoing, super-friendly, and asked me about 3 basic interview questions before asking me to ask her questions about Yale. I asked her everything I could think of- good thing I'd prepared questions, or the interview would have lasted about 5 minutes... :-)
If I could do it over again, I don't think there's anything I would have done differently. I prepared for a lot of questions, including some tough ones, and I think it's good to over-prepare for interviews in case you do get thrown a curveball.