I think you MUST ask at least one intelligent question that shows that you have given real thought to the school. Consider that you may have multiple acceptances, and you will have to decide between this school and some other school, what information do you want to know?
Just make sure NOT to ask something that you could have found out with a little research. Questions like, "What is this schools biggest weakness and what is being done to correct it." are good questions that can get the interviewer talking (and give you interesting information. Other good questions, "When you asked me _____ I am curious how you would have answered." might give you insight into a good possible answer.
Other questions, "May I see your match list" is always a good one.
If you know which two schools you will likely be choosing between, straight up ask the interviewer - if choosing between this program, and program X, what advantages does your program have that program X does not have.
You may also ask about the local area if you are unfamiliar. "What neighborhood do medical students tend to live in?"
If you are interviewing at a school affiliated with a church, you may ask how the affiliation affect patient care with regards to teaching about contraception, abortion, etc.
What are the opportunities for patient care and service outside of the classroom? Are there opportunities to get an MPH? Do research?
Have any students in the past done anything of note during the summer off?
Hmm.. there are a lot of questions, and I would make sure to ask at least one - shows that you are awake.