In my early days, I thought tipping was a bad idea, but I went along most of the time with a very large variance in how I tipped. I basically agreed with Mr. Pink's opinion expressed in "Reservoir Dogs."
What I didn't know at the time was that it's legal for restaurant owners to pay less than minimum wage, counting on tips to make up the difference. In this light, tipping is not so optional.
The question I run into most often is whether to tip on tax or not. The Straight Dope answered this question in "Should a restaurant tip be based on the check before or after tax?" It says, basically:
- You don't know what the waiter is expecting.
- It's better to (perhaps) overtip a little than (perhaps) disappoint.
- The cash difference is minor.
Here are a few other pages with still more to say about this hot topic:
- What is the origin of tipping?
- Tips on tipping references Emily Post and says it's on the full bill.
- tipping.org says it's all totally optional and has a restaurant page (and lots of other pages about tipping other people).
- The Stained Apron, a site for food servers, is very clear: total bill, 15-20%
- Techniques used to get more tips. I've read that the only one that works is to turn tables faster, thereby getting more customers.