[Zero10]

I don't know about in the US, but it is a little bit different around here....
Normally I'll tip 10-15%, of course you only tip at full service resteraunts (i.e. not at subway), if I have received mediocre service I will tip 5-10%, and bad service usually gets 2 cents.
Looking around at what other people tip, I am on the generous side.
A general rule I follow is to round up to the next round number above 10%, normally this results in 12-15%, another easy rule is to double the GST.
Waiters/waitresses are paid at least minimum wage plus tips, so you aren't going to put them below the poverty line by not tipping, tipping is a bonus.
Lots of my friends work at local resteraunts and bars, and they make more money in 3-4 hours of work a night then I make at my 8-10 hour per day job.