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> Tipping, as I understand it, used to be a voluntary thing. You left a tip if the service was exceptional. If it was only adequate, no tip. >
> -- Dave

Dave,
I haven't read all the other replies, so what I say here may have already been said. You answered most of your own questions. Tip well for excellent service, tip 15% for good service, tip small for fair service and don't tip at all for bad service. Sometimes the service is so bad the waiter should tip the customer, but they don't.

A good tip really pays off if you are a repeat customer. If you stiff the waiter, don't go back there for a while. Turnover in the food service business is often only a few months, so after that long, it might be safe. If you think tipping in restaurants is bad news, don't go on a cruise.
Howard