At the hotel I've been staying at (a Marriott Courtyard) Mon-Thu nearly every week for the last 2 years, I've requested a refrigerator for my room. Once in a great while, they forget to deliver it. When I remind the front desk and the houseman subsequently shows up with it, I usually give him a few bucks.

It's rare that I get to show anyone other than the housekeeper my appreciation for the work they do, so I think a tip is in order if service is, for the most part, good.