I'll do it if I have to, but I don't like it. I drive a manual transmission and valets (at least the college-aged ones you see at a lot of restaurants and country clubs near me) often don't really know what they're doing with them.
My dad was a valet for a while, and back in the time he had opposite problem, as he told me. Someone drove there with expensive car from abroad. It had automatic transmission. He couldn't figure out even how to un-brake it. After playing with it for a few minutes he finally managed to somehow very slowly get the car moving and move it to the garage or wherever they parked them.