Thanking the bus driver?

Do you thank the bus driver? If yes why do you do it? Some argue he's not doing you a favor so you shouldn't.

I have a habit of just thanking people without thinking about it. It's one of those things that can't be said too much, and even if the level of gratitude is almost non-existent, just signifying that you recognize a kindness could make someone's day a little better... Especially if you're driving a bus for a living. I mean jeez, I feel grateful to just get out of town after a shift at the hospital, and yet these guys drive that filth around all day every day.