I just wanted to say that there are good things about group study (assuming that everyone studies ahead of time). Your friends can help you with the topics that you have trouble with, and more importantly, you get a chance to explain the topics that you know well to your friends. There is nothing that forces you to synthesize and distill what you have learned like being asked to teach it to someone else. It's one of the best ways of cementing something in the brain.
Yes, the MCAT is mostly about doing practice problems, and that is an individual activity. But going over your mistakes with someone else is great because it gives you a new perspective. Even in fairly mathematical subjects like Physics, there are a hundred and one different ways to attack a problem. The more of them you know, the better equipped you are for any curve balls you may run into on the actual exam.
IMO, a good ratio of independent study to group study is 10:1.