I never give my car to valet.
The horror stories from my friends' experiences is enough.
Friend of mine's new M3 was spotted by his gf picking up girls. Turns out it was valet.
When they get busy, they leave the keys in the car, in the ignition, on the street. (friend of mine who works in insurance told me you'd be amazed how many cars get stolen this way)
Friend of mine had his clutch burned.
Accidents, and not minor ones.. like total loss (from my friend who is in insurance)
some have been caught drag racing.