DH and I were there last August (2-7). Had a great time! Yes, it was hot, humid, but not much different from the DC area where we live. Just drank more water and found cool off spots.
Fastpass was a blessing. We did everything we wanted at MK and the longest FP line we had to stand in was 20 minutes for Buzz. But that is because everyone with the FP showed up right at the beginning of the time, and all at once it seemed. We decided to jump in line anyway. The best FP experience was for BTMR. We picked up the FP, went to eat, came back a short while into our window to ride, and just kept walking. The stand-by line sign said over a 2 hour wait, we were literally in and through the line, and on and off the ride in 11 minutes...I timed it. Truely amazing!
We didn't have too much of a problem with the crowds. And we didn't follow any real tour plan, or get there early at any of the parks. Just used the FP. I would totally do it again, and am in July 2007 with DH, DS (will be 4) and my sisters in law (they will be 11 and 13). FP here we come!!!!!