I'm not a HEAVY sweater, but I do use anti-persperant/deodorant combos...
I have never had them fog to the point where I had to "fan" them. On humid days I've had some minor fogging around the edges of the lens, but it is well ventilated. I think Jason had bad fogging experiences with these, but he may not yet be ready to openly discuss them. The therapy isn't concluded, and it's still very near to him...
In short, I LOVE my goggles. Back when I had to sell off all of my gear, they were the only gear I kept.