Past trends posted in some of the guidebooks shows that summer crowds don't start to form until June.
However, Disney had good attendance last year, and there are good indicators that it will be even better this year. We are arriving on May 21, and when I called LAST MONTH to reserve our rooms at AKL, NO STANDARD VIEW ROOMS were available. I had to pay more to book a pool view room. This hurt my budget a little, but I found a way to balance it out.
So, I would predict...be prepared for good crowds.