Business travel - I leave 0$ about 99% of the time. Sometimes there will be something that they will do which warrants a tip and this tends to happen more so with concierge lounge attendants rather than with maids.

Pleasure travel - I leave a tip...2-3$ per day.

I'm bothered ever so slightly by the whole tipping thing....Perhaps part of it is my personal experience with going from poverty and living on foodstamps and not having many luxuries in life to a half decent job and life style, that I look at it as a personal choice they make.

If they want to be successful, they can be and there's no need for me to subsidize their lack of desire for a better future. I tip usually because the person is doing something I don't have the skillset or desire to do. If they are providing a service they are employed to do (be it a Starbucks barrister to a maid) they are only doing their job.