We been during August three or four times, and will return August 2012. Trying to fit everyones schedules we only have a two or three week window where all four of us are free. Wife and I are more flexible than 17 and 19 year old children!
It is hot in August at Disney, but it is also hot and humid in NJ during August. Bring plenty of sun screen, expect it to rain briefly every day, drink plenty of fluids, relax and don't over do it. Crowds are a bit lighter, although the pools are crowded. Enjoy!