Profusely. And quickly. I can't get through a warm up before it starts.
I've always done so, but it's worse now that my workout room is over the garage. It gets quite toasty up there in the summer. Last year, I was doing a three hour Spinerval, had the fan on high and blowing right on me, was wearing a rolled up bandana as a sweat-band (always have one on), and still whenever I would let my head drop forward, rivers of sweat were dripping off my head. I actually thought there was a leak in the ceiling. When I got off the bike and started walking, my socks were making a squishing noise. I felt a drip on my leg and thought it was my hair, so I pulled my hair around to the front but I could still feel the drip. Turns out it was my top. A steady drip, drip, drip.
Can you imagine how much I would have been sweating if I had been outside?