I run a fan aswell. I can sweat just thinking about sweating... I find the fan helps quite a bit. The only complaint is the fan damages/dimples the goggle lense. 509 fan in 509 sinisters.
Two guys in our group have them and can't wear goggles without them. I guess I've been lucky my Scott's don't fog on me but they both had problems with their 509s before the fans.
5 yrs with Habervision fans, have 3 pairs, too loud for snow skiing, don't hear them much on a sled though, web site orders have all been seamless, I recommend trying them.
Yep, I have the 509 fan in both pairs of Aviators, works great for me, doesnt fit well in the old style sinisters tho... Altho the buzzing drives me nuts when i can hear it