>If the service is normal, I will tip %10-%15. If it is great, then 20%, if it is poor, then nothing. I think it is best to send a clear message to the server. Then they can decide to change jobs or change attitude.

That's a US/Canada difference. Canadians tip less. I suspect that waitstaff in Canada are better paid than here in the US.

The key thing to remember about tipping in a US restaurant is that waiters are paid very little and the tips are a major part of what they earn.

Tamar