Below is a link to a Hotjobs article on tough interview questions.
From our experience in the resume and recruiting industry the toughest questions a hiring manager will make a hiring decision on are often the ones about your own career. People often think how you answer the “if you were a tree, what kind of tree would you be?” question may end up getting you the job but the truth is not really.
What we always say is have a story for EVERYTHING. Why you changed jobs, why you changed them so often, not so often, why you decided on a particular field and whatever it may be, have a story for it. Not saying anything is about the worse thing you can do so always have a story ready that explains your career history.