We have been the exact same time (1st week of May) the last two years in a row. PERFECT!!!!
Speaking for our 2004 trip - crowds WONDERFUL - walked on several rides. Minimal waits for others. Weather GREAT - was nice and cool in the evenings and not too hot during the day (upper 80's). Only wait times of any significance where for the attractions that seem to always have wait times no matter when you go. (Test track, Splash Mountain, etc)
Our 2003 trip - slightly bigger crowds but still great!!! Weather very HOT that trip - it was in the 90's for that whole trip.
We will be going again this same time. Hoping for the great weather again and small crowds. We don't go later in May just to "try" to avoid any hotter weather.
Hope that helps!
Heather