I never used to sweat while drumming until recently where I've just thought "screw it" and just got absolutely laid into the kit.
I'm considering drumming in shorts/ 3/4 lengths and a tank top or something.
The past few gigs I've had the sweat beating off me - I don't even sweat that much when I play a 90 minute Football (soccer) match!
What also becomes a problem is keeping my ear buds in - they keep wanting to slip out. Annoying.
I don't sweat too much if its simple stuff, but if I get really busy on the kit giving it everything I got, i'll sweat on the back of my head and neck. That's weird because when I do hard work, i usually sweat on my forehead and temples.