We always go right around this each year -- right after our schools get out. Be forewarned that it is HOT, HOT, HOT already. This past year, the parks were pretty crowded -- but do-able in the mornings. Memorial Weekend was absolutely CRAZY -- everything within 30 minutes of WDW was completely booked. It rained a little bit in the late afternoons, but these were the typical quick warm weather storms -- over before you knew it. While it's definitely NOT an off-season time to visit any longer, we still enjoy it very much.
Note: The crowdes at the end of July and beginning of August this past summer were much lighter than during our May trip.