Kaydubz: I was just like you, an A student used to staying up the night before cramming, but when I was studying for the New York bar exam, I stayed up all night the night before reviewing, and due to the added stress of the exam, the four hours straight of multiple choice, and my lack of sleep, to my ultimate HORROR I found myself inexplicably waking up DURING the exam itself. I had fallen asleep! This was years ago, and I don't remember how long I was asleep for or even when I fell asleep, but let me tell you, it wasn't pretty and it's not worth it to stay up the night before studying, even if you think it might help. You need your rest and concentration for an exam like this.
Even if you decide not to stay up all night, but to, say, just study until 6pm or 8pm the night before, you may find that you're so worked up that you then can't fall asleep. Same result. Know what I mean?
I'm taking it this Friday and my plan is to continue reviewing formulas and such all day tomorrow, and taking all of Thursday off (although I may take a quick look at my formula sheet in the afternoon), and certainly not looking at anything MCAT related on Friday before my 1:30pm test. I actually specifically picked the 1:30pm time so that just in case I've got a case of nerves the night before and can't sleep, hopefully I can sleep in in the morning.
Luck to all!