Idle curiosity here...

In restaurants, I prefer to tip always, and tip well (usually 20 percent or more) because I think that that waiters and waitresses have a difficult but low-paying job which is frequently full of rude, surly, condescending customers. I want to be the bright spot in their day, so I treat them nicely even (and perhaps especially) when they make a mistake, and always tip well.

But I know some people who use tipping as a merit system, like the guy in the video clip. There's logic to using tipping as a service-quality indicator, but I happen to disagree with it.

So what I'm wondering is... For those of you who have worked in a "tipping" job (waitstaff, hotel bellboy, valet, etc.), how do *you* tip? Do you follow the "tipping as a merit system" logic, where you only tip (or only tip well) if you feel they did a good job? Or do you, knowing how sucky the job is, always just tip well because you know what they're going through?

I ask because I've never had to work for tips before, and I don't have the point-of-view experience.