Not too bad if you plan your day right. This is our 3rd trip in late August (previously here in 2002 and 2004) and it is busier this year than in the past. However, if you get to the parks early and use Fastpass well, you should be OK. We were at MK yesterday, and arrived at about 9:45, which is later than we usually do. We got Fastpasses for Pooh right away, which were for 11. By 11, we rode Dumbo, the Carousel and saw Mickey's PhilharMagic. Before we rode Pooh, we got Fastpasses for Peter Pan. We then did the Teacups and went to Toontown before we rode Peter Pan.
By 3, the Standby wait for Splash Mountain said 100 minutes. However, there were still Fastpasses available for 5:30. The standby wait for Space Mountain at 5:00 was 80 minutes, again Fastpasses were still available. Even with FPs, we waited 15 minutes.