That's an intriguing idea. I too would like to hear comments from anyone with experience on this issue. It seems like a lot of time is wasted in perfectly filling out the ovals, I estimate approximately 2 minutes of time that could instead be spent on the exam.
Yeah, I know some people in my Kaplan class who have been doing this....they say they've always done it for every multiple choice test and never had a problem with it because as long as the scanner can pick up the #2 pencil mark, they are fine.
I once had a teacher who worked at a standardized testing center and she said that you didn't even need to fill it in half way. Just a dark mark in the center was sufficient. Though, with something as important as the MCAT I don't know if I would take that sort of a risk. Who knows, even if you get it graded by hand, you might get some anal person who says that your answer is wrong because you didn't fill it in all the way.