We were there last year the 8th through the 13th. The crowds were great and practically non-exhistant. Most rides were less than a 10 minute wait, and during some times the big rides (tower of terror, Rock'N Roller Coaster, Test Track) were walk on (you went straight into the pre-show). We weren't planning on going back until next year, but with this Fairytale package.... we're going to go again this September.
Oh yeah..... the only thing to keep in mind is the heat. It was VERY hot and muggy... but manageable if you are careful.