May before Memorial Day is wonderful!
We've gone 3 times in May, including 2007. We like to go in the week before Memorial Weekend (usually checking out on Saturday of Memorial Weekend) so it's about 7-10 days later than you're talking about. May is a wonderful time to go. Even when it rains, it's the summer weather pattern (quick cloudbursts, then stops.) Plenty warm enough to swim (mid to upper 80's, but not the killer heat of mid-summer.) Crowds are very manageable because most U.S. children are still in school. Not the lightest crowds of the year, but far from overcrowded. We're going again this year, arrival 5/19 at POFQ (can't wait...12 1/2 weeks!)