Unfortunately, since I'm a teacher, we are only able to go during the summer. We always go the 3rd week of August because the prices drop that week and I don't have to be back for work week until the last week of August. I guess in 18 more years when I'm able to retire we will be able to go in September to see the fall decorations and in December to see Christmas.
DH and I were there Aug. 19-23 this year and it was hot but I didn't think it was unbearable...we left the park everyday around 1 or 2 to go to the pool and rest and returned about 4 or 5 so we missed most of the hottest part of the day. And there are a lot of rides/attractions that have lines inside a cool building so we were not bothered.
We did have to deal with a lot of rain this trip...went in 2009 during the same week of August and it only rained on us 2 times in our 7 day stay. We have a CM friend who moved down and started right before we left last month and his comment when I asked him what to expect was, "I can guarantee it will rain everyday at 4pm." Well, the first day we were down there (19th) it stormed at 3:00, 6:00, 7:30, and 9:00...they had to postpone Wishes until the storm passed. The next day we were at HS and there was a storm in the middle of the aternoon (while we were back at the resort) and another "deluge" during EMH at 11pm...we ended up getting soaked while waiting for our bus to go back to ASMu.