I always ask this question, just so that I have a question to ask.
"Everyone has such great things to say about the school, but if there were one thing you didn't like, or one thing you would change, what would it be and why?"
Most of the answers I've gotten on this are either really drawn out (one interviewer said if you asked this of everyone, you'd get some little, minute thing that differs from person to person, so there's nothing glaringly wrong with the school), or say something like "Well, this was a problem I did have, but the school and/or community has addressed it now."
It's also a good fallback to ask about away rotations; how much flexibility there is for clerkships, say, back where you're from or internationally. I asked one interviewer if there were any required clerkships based on location, such as rural areas (vs. the specialties themselves) as there are at some other schools. She went on about how nothing was required, but the opportunities were certainly there if you wanted to go that route.