Well, I will chime in.
We did the end of August last summer. Arrived on August 23 and left on September 1.
The Bad: It was hot! The first couple days it was 100 degrees. (But then it cooled down in to the mid 80's, which to me is perfect.) But, it didn't bother us too much. We took breaks in the afternoon to swim and went back into the parks every night around dinner time.
The Good: Lots of schools start in mid-August in SoCal. Weekdays the lines were pretty good. 5 minute wait on Pirates, 15 minute wait on Thunder Mountain. The worst lines are Space Mountain and Toy Story Mania. Luckily with Space Mountain, just use fast pass and you will be fine. Dining in Downtown Disney didn't require reservations, it was walk in and be seated within 5 minutes (we even had a party of 14 one day!) No problem.
There was LOTS of speculation on how HORRIBLE it was going to be last summer after the block of AP's would be lifted. This NEVER really materialzed. We were prepared for the worst, and delighted at how few people were really in the parks (compared to the speculation!)
Let me just say, that it is still summer. There will be crowds....but last year it was very managable, I dare say even nice.
I love end of August. You are pretty much guaranteed nice, warm weather and there are long hours every day. 8:00 a.m. - Midnight.
If I can convince my DH, we will be there again at the end of August this year.