We were there labor day 2002. The weekend itself was fairly busy. After that, no one. If you can stick around a few days after the weekend is over, the crowds are pretty much gone. (Well, it is Disney, so there are still plenty of people, but the longest line wait we had was 15 minutes).
2 lousy seasonal things for Florida. 1. Hurricane season. Usually this just means rain for Orlando (except last year, ouch!) 2. Love bugs. They don't bite, sting, or really do anything besides just be everywhere. Personally, I don't mind them, but they really are everywhere.