Chad,
It's interesting that you asked this question in the Pitching forum, and I would love to hear any reports of how this has worked for pitchers.
I have seen visualization work! I played for a very good basketball coach in HS. (He was also scary - our school disciplinarian and football coach, and he looked like a pro wrestler.) One year he had us use visualization, and I specifically remember when we focused on free throws. Several times per day, and especially at night just before going to sleep, we would visualize ourselves shooting free throw after free throw, and see the ball going in perfectly, hear the swish. Our team free throw percentage went up significantly!