We've been to Disney twice during Thanksgiving and once in August. We stayed at the beach club in August and really liked it. We're going back this August - can't wait!
It's definitely hot in August, but absolutely manageable. Get to the parks at rope drop, leave around 12:30 for an afternoon at the beach club, and then back to the parks for dinner (or just after).
We all carried "camelbaks" and wet through approximately 3liters of water a day! Hydration, comfortable clothing and shoes, and down time in the afternon are all key.
When we went in mid-August (8/17 - 8/24), it was less crowded than Thanksgiving. Thanksgiving week is ok until Wednesday afternoon, then the madness begins until Sunday.
Besides being a little less crowded, I also really liked going in August because we LOVE the waterparks. The only EMH that we take advantage of are the EMH for waterparks. EMH evenings at Typhoon Lagoon are fantastic (no crowds - at all) and the mornings (although early) are great as well. My kids were able to go down Summit Plummit (Blizzard Beach) three times during the EMH and the lines in the morning are very minimal.
BUT...if you don't think that you'll be able to get to the parks until late morning, or even noon, I would re-think August. The parks (particularly Animal Kingdom) are really tough in the mid-day summer sun.