Ok, here's my experience....I've applied to medical school on two different occasions. Both times, I took the MCAT for the first time in August. Both times I got at least 1 acceptance. The key is to get everything else in early. The MCAT scores will be in by October and your application will be sitting pretty for the second (or third) wave of interviews.
IMO, it's more important to do well than to worry about when you take it. I signed up for the April MCAT when I decided to apply for the 2004 entering class. I wasn't ready and ended up requesting a refund. By August, I was much better prepared and ended up getting a good score. (First time around, it was just a late decision to apply and I had missed the deadline for April).
If the rest of your app is pretty solid and you can get all your transcripts and applications in before you take the test, then I would think you'd still be in good shape to get in for next fall!
Good luck.
Willow