This is something I have thought about as well. I honestly never tip chambermaids, although I suppose that I should. I always tip doormen when they hail me a cab ($1-2) and more when they load/unload luggage ($5). I also tip the concierge if they go out of their way to get me a reservation at a restaurant that claims to be booked up, or if they score me some good tickets ($5-10).

I was at the Park Hyatt in LA last week and the maid walked in on me as I was getting out of the shower...I probably should have tipped her!