We went in 2004 in June. I think we were there June 12-18. The crowds weren't bad. We especially enjoyed Star Wars weekend.
I don't like heat, but it didn't bother me much. It seemd like we were always entering someplace with a/c. We did carry water and drank lots of it. We'd head back to the resort in the late afternoon and swim and/or relax. There was a threat of a thunderstorm everyday, and it rained most days during the late afternoon. It was never a problem.