What matters most to you, and why?
EDIT: TL has already post this question 
But if seriously... I almost sure that I would ask: If you were me what directions would you focus on during study in order to get maximum benefits from the MBA program? or a slightly modified question depending on overall impression.
I don't think that question like "What do you look for in an applicant" will add value in your interview. I'm almost sure that Dean answers every day that question and will say automatically maybe even word-by-word from school site. The question does not force him/her to think a lot and you will look like many others.
In my question, Dean should take my side even for a few seconds. Actually I ask him or her to play for me. Moreover the question will force to think, maybe even to think for a while as each of us is a unique person with own set of skills and experiences. Additionally, in the question you passes through choice, in other words, you ask as you have already admitted. Do you see the difference between: "Would you like to buy a car, or not?" and "Would you like to buy red or black car?". You also have a chance to get a really good personal advice from successful manager who is better than any admission consultant . Finally, the first and last words are more important because their more memorable. So too is your last question.
too many thoughts about simple question? At least it gives me a bit confidence