Hi all. With interview season in full bloom, this question is surely one that has or will come up in an interview. Many find it a difficult one to answer due to its sheer broadness. If you haven't seen it already, I found the below link that breaks it down and helps guide the interviewee to a structured approach. The brief article is written by an MD and is geared for pre-med. However, the approach is the same for us. I hope it helps..
http://studentdoctor.net/2008/02/trick-question/
http://studentdoctor.net/2008/02/trick-question/