Having both worked in tipped occupations and being a frequent diner-out, I’ve seen both sides of the equation, and I gotta say, yerba has a legitimate point.
See, it’s been my experience that except for certain unusual circumstances, (extaordinarily good or extremely bad service) a tip, and the amount tipped, is not a reflection of how good the service was. It’s a reflection of how generous the person doing the tipping is.
I’ve been stiffed too many times, and seen too many coworkers stiffed, when I/they/we busted ass giving great service, and seen many people tip generously when they got nothing more than average polite service.
I have twice not tipped waitresses, once because despite the fact I was the only customer in her section, service was extremely slow and the waitress was totally inattentive, once because the waitress was downright rude. I also once tipped a waiter more than the cost of my meal because on a busy night, he went above and beyond what I could have reasonably expected (it involved a casino restaraunt where the union rules demanded that a cocktail server be brought in from a foriegn country to bring me a simple glass of wine, which had to be paid for in cash, and since I only had enough cash for bus fare home and was paying for my meal on my debit card, well… to make is short, the waiter made damn good and sure I got my wine, and I made damn good and sure he knew I appreciated it).
I generally tip around 20%, more if the service is exceptional, but if it isn’t all that, I don’t tip less. If it’s really, really bad, I don’t tip at all. But really, I’m the exception. Most people are going to tip what they’re going to tip, no matter how good the service is. So, yes, I think it’s up to the restaurant to evaluate the server’s job performance and pay him/her accordingly. The customers, by and large, don’t.
But then again, neither do most employers.