Hi,
We've been for a few summers (August) now - last year was the quietest ever - the year before heaving! As pointed out earlier, every-one is off in August including Spansih, French, English although given the exchange rate perhaps not so many of the latter!
That said it hasn't ever been full unlike at Xmas this year but it is busy and expect to queue for the rides and either use EMH if at a Disney hotel or perhaps buy extra Fastpass tickets off ebay....
Only you can judge whether the crowds are acceptable....it hasn't put me off!
Rgds
A