We always leave a couple of dollars on the bed for the cleanning service when staying in a hotel.
I always leave a little extra money, if we need extra towels or washcloths.
I always keep my hotel rooms clean. I leave a tip if I need something additional (ie: usually I ask for an extra blanket for the bed). But I don't leave tips for normal day-to-day work.
I know I'm in the minority on that, but frankly, I'm just not a tipper. I think the whole premise of giving someone extra money for something they are supposed to do anyway is dumb.