This past August was our first time at WDW in the summer months. Previously as a family we had been there in Oct, Feb and several times in April. We couldn't go any other time because we had camping plans with relatives in June, a family wedding in CA in July - so August was the only viable month.
Honestly, I was worried about the heat and the crowds. I lived in Florida for a few years and hated the heat, but we did fine in August. It was very hot, and we were uncomfortable, but it never slowed us down. And the crowds were so much less than we had been used to in April that we're considering going in August this year again.
Of course later in the summer you could run into a hurricane, but we had better weather in Fl that last week in August than they did back home on the Cape and Islands where we would normally be. I would chance it again. The parks were so much more manageable and reservations were so much easier to get.