I'm under the impression that, if the wage paid plus the tips earned do not equal minimum wage, the restaurant has to make up the difference. Thus, tips are taxable income.
That said, I feel no compuncture against leaving no tip if the waitress/waiter is terrible at their job - a recent example would be when, during a two-hour visit to Steak 'n' Shake, we saw our waitress all of three times - once to take our order, once for refills, and once to bring our food out to us. She spent the rest of the time cleaning the area around us and doing a pretty damn good job of avoiding our attempts to flag her down (which included one of us waving their arms quite a bit).
However, her shift ended about twenty minutes before we left, and the waitress who took over for her was much more attentive; thus, she received a 30% tip.
the idiot is the person who follows the idiot and your not following me your insulting me your following the path of a idiot so that makes you the idiot - LC Tusken