It's out there. "Wired" magazine ran an article about how anyone can have a key made by simply taking a photo of it. And people are sounding alarm bells about how a valet could easily copy your house key.
Well, it's stupid to give them your house key to begin with, not because of the home break-in potential, but because valet services DO lose keys. Sometimes, at some valet services, it's almost a matter of routine that customer keys go missing. (No kidding.)
You should only give the ONE key necessary to operate the car when using a valet service. Don't give them the keys to your life.
Are they going to copy your house key? It's highly unlikely. However, I wouldn't leave spare change in your cupholder, or sticks of chewing gum, or Chapstick.
They'll take your "blunt." Some will take your fancy sunglasses. They might take your handgun. But is a poorly paid valet going to spend 6 bucks to have a house key copied? I very much doubt it. Though it is remotely possible. So don't give it to them. And take that garage door opener out of your car too.
REAL PRO TIP: Leave no items of value inside the car when valet parking. And keep a spare car key with you.