We have been there the 1st week of May for the last 2 years. The weather was beautiful. This year though, we noticed that the evenings were cooler than 2004 & we did wear slacks & long sleeves once the sun went down. My DS7 was actually so chilly one night in MK around 10 pm (it was open til 1am) that we ended up just returning to our hotel.
We did notice more crowds in 2005 as well, but everything was still quite manageable. The lines were not bad..but we use FASTPASS a lot, for the rides where it was available.
We're actually going the 1st week of May again next year.
It has been a great time to go.
Hope it is again in 2006 for the both of us!