As my sig says, we were there Feb 25 - March 4 of 2003. We find it to be extremely comfortable, low to mid 70's. I can't believe some people would venture to Florida in July or August. I'd pass out! But anyhow.. I was actually just looking at my pictures tonight from 2003 and in addition to what I can remember, it rained 2 of the 8 days we were there. If memory serves, typical Florida rain storm that clears up after 15 minutes. Though, the sky was quite grey in a number of these shots on the days it rained, so i'm inclined to believe the sun didn't pop back out all to often.
As for crowd levels, low-mid from what I can remember. I remember going a few years back with my parents and grandparents in June (again, why? It's HOT!) and it was packed. I don't think we waited more than ~20-25 minutes to ride anything at WDW and a very small wait for anything food related.