We went this past May 5-9th. It was glorious (at least compared to the winter-like weather we left in upstate NY). Temps reached a high of upper 80's to 90's, the humidity was mild. On the 5th, we arrived at night to rain. In the morning, it was a bit overcast, a bit chilly ... but by 2pm, it was gorgeous!!! Sun was out, nice and warm. The last two days were just amazing -- hot and sunny! Crowds weren't bad, either. It's the only time I've been to WDW and had a 15 min. wait for ToT!!! Usually, the waits are like 75+ mins.!!
The only other time we went in May was in 2000 and it was beautiful every single day! We were there later May for Star Wars Weekend and the crowds weren't bad. I think the crowds were bad this SWW b/c of the release of the last movie in the series and all the furvor it created!? Just a guess. When we went, Star Wars Episode I had been released a few weeks prior and it wasn't as packed as I've been reading this year has been! Go figure!!!
I'd choose to go in May again. I'm lucky that we have a long weekend (not Memorial Day) at my school and am able to go. I'd love to be there longer, but as a teacher, I can't take the time off.