Between reading Nickel and Dimed and my future sister-in-law having worked in the hotel industry I always tip hotel cleaners. Talk about people who don't make enough money for what they're required to put up with. And I can't imagine not tipping food delivery people; if we have enough for the pizza but not the tip we just don't order. It's just not done.

I over-tip cab drivers, but that's mostly because getting out of a cab is not when I want to be figuring out percentages.:)