We went during the last week of August 08 and it was great. It was hot and it rained everyday, but there weren't any crowds. We didn't have to wait in long lines for almost anything. If fact we had extra fastpasses (since we bought into
DVC that year) and we came home with most of them.
This year we went in July and it was miserable. The heat was unbearable and the crowds were awful. We decided if we go back in the summer, late August is the time to go. (
Just don't let the rain ruin your vacation).