My son and I went last year during the President's Day week...and it wasn't as crowded as I expected. The lines really weren't that bad, and for the rides that I really wanted to go on...I grabbed a fastpass. The fact that the weather was warm and that I was not home and at work helped too!!
We then went again in October...and that was not as pleasant. It was too hot and humid and the parks seemed more crowded. But, my son found Disney Quest and that was the end of the hot days in the park! We had a lot of fun there and just hanging out at the hotel and the water parks!
If you are prepared for the crowds...it will be easier.