Should you tip the waitress

EDIT: It depends on where you live. In North America you should ALWAYS tip even if you think you received poor service (just tip less, like 5% rather than 15-20%). Your waitress/waiter is getting paid LESS per hour than the normal minimum wage, because the governement assumes they will be getting tipped. In some places, your server will be making as little as $2/hour. Additionally, they will have to "tip out" approximately 4% of their total sales to the kitchen, hostess/hosts, bartenders and support staff. So essentially they have to PAY to wait on your table, whether you tip them or not. So I emplore you to always tip SOMETHING, even if it is just a little.

Elsewhere (Europe, Australia, etc):

it depends on what type of service you get. if she makes a good effort to look after your table and you feel happy with the service, then yes you definitely should tip the waitress. even if its only something small, to me, the fact that my customers are happy enough to leave a tip means more than the money itself. on the other hand if she is rude, unfriendly and appears to be making no effort at all, then it would be hard to enjoy the meal so you should only tip if you are happy with the service.