I think that this question is posed mainly to determine whether you see your self as a leader or as a follower. I think that, whatever you decide to answer, it should present yourself as someone who is looking to lead. Medical schools want alumni who can accomplish great things and carry the medical school name with them. Realistically, ten years from now most of us will be finishing residencies, fellowships, or will be recent attendings. However, in ten years you could also be well on your way to succesfully...blah blah.
Also, don't be afraid to speak of your life outside of medicine. They want commitment, but they also want to know that you will be seeking fulfillment through other aspects of your life such as travel, family, hobbies, etc.
Anyway, one of my mentors clued me in on the leader/follow approach and it helped me quite a bit.
In ten years from now I will be laying on my hands and healing the sick, raising the dead, and selling presciptions for pain killers to high school kids.
