I tip roomservice, bellboys, and parking attendants if I have a 2 or more night stay, b/c it is likely I will run into the same person again...so I want to be nice. If it is a one night in a hotel I will never go to again, then I don't. I might even give 2 bucks if the person is extra nice/cool.

I never tip maids cuz to me they are anonymous. And usually I come back to the hotel pretty late, after they have already turned down.