My experience is similar to RiftTraveler's. Customers who are using a gift certificate, or who get some other type of discount (like a free birthday dessert) tip mostly on the full amount of the bill or even a little more.

However, take a customer's steak off a check because it was overcooked, and he'll almost never include the cost of the steak when figuring the tip. People sometimes seem to have this idea that it's the server's job to cut open the steak to check how it's done, or to stick her fingers in the food to make sure it's hot. I don't get the mentality that says those things are *my* fault.

Think of it this way- the dollar value of the food represents, roughly, the amount of work the waiter put in to take care of you. So whether you actually pay the full amount or not, you should tip according to the amount of work that was done.

For myself, I overtip, almost always. If I get particularly bad service I will have to force myself to leave as low as a 15% tip. Being a waitress myself I know that an extra dollar or two from me- which is really not that much- will brighten the server's day a good deal.

While I agree that the way tipped employees are paid and how they have to rely on tips is not the best system, in general it works out significantly better for me than if I were paid minimum wage, so I'm not complaining. Especially since now I work in a restaurant where the customers who repeatedly don't tip properly are asked not to come back. :-}

I've heard a few times that leaving a penny heads-up on the table is supposed to indicate good service. Does anyone actually do that? I sometimes find head-sup pennies on my tables when I bus them, but for some reasin I'm inclined to think that people just left them by accident.