Did it this year - a family birthday fell that week - and it was crowded! But the weather was nice. But if you plan - and look at crowd calendars like Touring Plans to give you an idea of which park is going to be in the red zone on a particular day - then you should be okay. Take advantage of those Extra Magic Hours, especially in the AM and know that dinner time can be the best time to ride some of the more popular rides since everyone else will be eating. And unless you want to wait for an hour to get on a bus back to your resort, leave the Magic Kingdom right around the start of the 3:00 PM parade... And in the evening, hang around for at least an hour after the end of Wishes as the park clears out after the fireworks and you will once again be waiting, waiting, waiting for that bus back to your resort, even though Disney has finally gotten smart and added more buses to handle the mass exodus after Wishes.
I take the crowds as a challenge - I survived the Brazilian Tour Group invasion in July - and a great time to people watch. Amazing what people will wear to a crowded public venue....