I have gone in March during Spring Break and dealt with high, high crowds. I would say that labor day when we went in 2012 was AMAZING. We arrived the day before labor day and stayed that whole week. We didn't use fast passes most days, and the days we did only grabbed a couple to ride our favorites multiple times. We were in Hollywood Studios that week and had a CM tell us that it was some of the slowest crowd levels in September he had seen. Even on labor day, which I believe we did AK and HS, the crowds were very managable. TSM obviously got to high wait times, but other than that it was great! It is a very hot week. In the 90s the whole week with humidity, but dealing with New England summers I was used to it. We are going again this September for the same week and cannot wait!