I'm pretty much in the same boat as Tracy. And I worked in the restaurant industry as a bartender and waiter for nine years. My rules are thus:
Tip for service when it's due, not when it's expected. If someone does a good job, give what is expected - whatever the standard in your area is. But be wary, often those standards are suggested by the very people serving you and working in the service industry. If someone does an exceptional job, tip them better than you normally would. If someone does a really crappy job, leave them nothing. Don't leave a few coins thinking you'll insult them, leave them nothing. Why? They'll get the picture much more clearly and won't just think you're a cheap idiot.
Most restaurants pay their employees minimum wage and the difference they make is based on incentives or tips, as we call them. Otherwise they starve, but you know what? If you're crappy at serving, you shouldn't get more just because you show up.
I can see merit in tipping at a buffet, initially I was thinking of a buffet where you walk in, pay and get pretty much everything yourself (we have those here) including your beverage which is non-alcoholic. But I think Scott is referring to a different type of restaurant than I was initially thinking and we do indeed tip there, because we order booze with the meal and they bring water and refill it, etc.
As for tipping at a pizza place when I pick up? It has merit, but again, it's based on merit. We often order from the "usual" place, so I tend to know the guys pretty well on a familiarity basis. Do I tip them? Yup, if stuffs ready when they say it is. It pays dividends in that we tend to get better prepared pizza because they remember the name and that we tip. We'll get extra toppings and have received larger pizzas for nothing in return. But I won't tip if you tell me 30 minutes, I show up in 35 and wait 20 more. I'll also tell you why though.
I much prefer places where the tip is factored into the meal price and the staff are reasonably compensated. I loathe serving staff that feel they deserve a tip though and I used to work with a lot of them. You earn it, not deserve it.
