We go pretty regularily during August since our kids have gotten to middle/high school age. It's just too difficult for them to try and make up the work in off season (though we prefer those times).
But overall, crowd-wise, we've seen just as large, if not larger, crowds during F&W Festival in November as we have in August. Yes, it's hot and humid, but it's the same in Philly at that time so we're pretty much aclimated to it. Yes, there are those afternoon thunderstorms but we expect them and don't fret over it. Our strategy is to get to the parks early (utilize EMH when possible), then leave to go back to the resort/pool in the heat of the afternoon. Plan a nice sit down dinner somewhere and then head back to the parks after 6 pm. This works for us. We'll be in WDW Aug 5-16 this summer.