Your regular hotel/restaurant valet basically lives on the tips (kind of like your waiter, but even more so), but in many residential buildings there is a strict 'no tip' policy for all staff including valet because it's a huge hassle for the tenants.
With that said, most of the employees will still accept a tip and you will get better service. I would double check with other residents or the onsite property manager for clarification.
As to the amount. The more generous you are, the better service you get (i.e. your car will always be parked at the front of the garage and you'll be out in no time), however, you can garner almost as much attention with a creative tip. For example, a folded $5 is nice, but an origami $2 bill in the shape of a bow tie or a heart or... will get you an equal amount of attention especially if delivered on a regular basis. Take a few minutes to learn to fold bills creatively and the boys and girls in valet will get to know you quickly. That with a charming personality should be all you need.
With that said, the guy who drives the Lambo and tips $20 every time will definitely get better service, but he's the rare exception.
Posted By: Heathergfe Next month I move to a high rise in Las Vegas. I have always lived in a house in the suburbs. At my new home there is valet parking ONLY. I assumed that every time I get my car I will have to tip. The real estate agent who manages the apartment said that I am not supposed to tip at all. She said that they get paid very well and it is part of the service charge for living there. I'm afraid she may have said that just to make the apartment seem more attractive. Does any one else have experience with this? I don't want to seem like the bitch who doesn't tip if I should. Also, if I should tip, what is the appropriate amount each time I get my car?