i'm also reapplying, and while at first i resisted it, i finally decided to write a completely new PS. here's how i looked at it:
-no one's going to think negatively if you have a different one (unless of course it is of much lower caliber than the first) but some of the schools you're reapplying MAY think "well why didn't this person redo his/her PS?" it could come across as lazy using the same one... plus, you don't even know for sure if your PS was part of the problem in your previous app
-how bad do you want this? as reapplicants i think we will be under more pressure to prove we have strengthened our apps. this includes the PS. plus, redoing it shows you are still serious and still passionate about medicine because you're putting the effort in to write a new and stronger one. let your determination and commitment to this shine through.
-you may find (as i did) that you know yourself and your motivations for medicine better than you did a year ago, especially if you've continued getting clinical experiences, and this should help you write a more personal and insightful PS.
really, overall, i think you have a lot more to gain in writing a new one, and not much to lose, compared to using the same one from last year w/the real potential of turning some adcoms off automatically. just think of it as something you have to do as opposed to something optional, and i think you may find it easier to write the new one. also, there's been other threads discussing it, i'd search the "reapplicants" forum if you want to get more feedback.
well that's my opinion, hope it helps. best of luck
