I usually don't pay attention to percentages. If I have a $10 meal and the service is good, I will usually leave a 5. If the service is horrible, I will leave a buck. If it's a $100 and the service is good, I would tip $20-$25, if it were horrible, I may leave 10-15.

My feeling is this, if you can't afford to tip the server, you can't afford to eat in a restaurant. Not to mention, servers only make around 2 bucks an hour, they are counting on tips to pay their rent.

Granted if they suck at waiting, they need to find a new job. You couldn't pay me enough to wait on hungry assholes again.