prmd, I had the same reaction as you when I got my second acceptance...if I'm holding two spots, aren't I cheating someone else out of a spot? Then I thought about it, and the answer is, well, not really. Schools almost always put way more people on their waitlists than they will open slots for. So even if you hold spots you wind up not taking, people will get offered the slots you give up later on. Maybe it will make things tougher for them in the end, but that's the price they pay for you being such a good candidate! 😀
Seriously, if that sounded mean it wasn't meant to be. All I'm saying is, I think we should be as nice as possible in this process, but not nice to our own detriment. If you have an acceptance in the bag and interview at another school you wind up not liking as much, by all means withdraw your app from there to give others a shot. But if you like two schools about the same, there's nothing wrong with waiting to see which comes through with the better financial aid offer. Check out AAMC's statement on the subject if you still have doubts...it helped assuage mine.