How tips work in a restaurant (no permalink, scroll to January the 28th)
"The real issue in the evolution of this meme is in its applicability. Tips work in an economic transaction where there is a one-to-one connection between a service provider and service consumer. When you move to courtney love's 1 billion people leaving tips it stops making sense."

I would like to point out that tips in restaurants are indeed a cultural practice (as shown in the introduction of Reservoir Dogs). Here in France, there's already a 15% obligatory charge on service, so you're not compelled at all to add a tip. You'll do it if the waiter was real nice or competent (and believe me, that happens less often than in the US), or if you want to show off you live the high life.