My son was shy of two when we went the first time. My daughter was a month shy of three.
I would say get your toddler prepared by watching the disney shows. If you don't have the Disney channel, rent some DVD's. By the time we went, my little guy was all about Tigger and Pooh, so that ride was really special for him.
At the 2 YO age, I would say that the biggest problem is that when they get tired...they just get tired. As they get older, you can distract them from being exhausted by doing something fun. WHen the finally get to the hotel, they crash, but you can manage them through that "one more ride" or that parade that you really want them to see. But with my son, when he was done - he was just done. It didn't matter that Winnie the Pooh was walking by, he was tired/hungry/hot/whatever.
We also went over Labor Day Weekend, which was HOT (August will be warmer). My daughter was okay, but my son is a little hotbox and was absolutely miserable. He also sprouted a low-grade fever, which made everything a little more exaggerated than they would have been otherwise. I will never forget sitting in Play n' Dine with my kids. My daughter couldn't get enough of June and Leo (she was BIG time into Little Einsteins) - but my son just wanted to sit in the AC and eat his waffle. He could care less...but try to take that sausage away and LOOK OUT.
Now, all that said -
Something magical happens between where my son was (17 months) and my daughter (35 months) - where the Magic Kingdom comes alive. Cinderella REALLY lives in that castle, and Mickey REALLY is a giant mouse. KWIM? Not only do they care - but nothing has been tainted by reality. I just eat this age up, because my daughter watches Aladdin (he current favorite princess movie) in awe. She really thinks Jasmine rode that flying carpet, and married her prince. She can hardly wait to visit the BBB in early October.
So, I would be prepared for a range of reactions when you take your toddler. Prepare for the "worst" - but you may be surprised!