Hi,
It depends I guess, we all have different tolerance levels.
The last 2 years we have been in August and whilst I was fine my wife and son found it too hot. The problem many of us have is July/August is the natural time to go because of the school holidays, and my wife is a teacher too.
We should have been in Orlando now but we actually moved the holiday to next Easter, purely for Joshua's benefit.
I reckon from 2009 we will be back on a July or August schedule mainly because for Julie teaching wise it's the best time to go.
The majority of people , or at least a fair percentage would not choose August as the ideal time to go, based on weather and crowd levels.
I am not being over-negative hopefully, anytime to go to Florida is a good time, the best advice is not to spend all day at the theme parks - I think it's vital to take a break in-between. Getting to the parks early means you beat the worst of the heat and it's quieter too.
All the restaurants, shops, attractions will be air-conditioned indoors, so be sure to take advantage, plus the usual advice drink plenty of water and wear loose comfortable clothing.
Taking things at a leisurely pace, having plenty of rest days will help too - I am sure you will be fine.