I can tell from experience if you come from a non-tipping country you can really have some negative experiences before you realize what's going on :)
That said, the "need" for a tip does make the waiter/ress a lot more pro-active and helpful than in my country where waiter/ress's can be cranky even. In the US they introduce themselves ("Hi I'm Jerome, I'm excited to be your waiter today!" Made me smile every time), make sure you are ok, the level of service is pretty high.
We do tip here (Netherlands), but it's more when service was really good. But personnel won't bat an eye when you don't. Of course, we learned from Reservoir Dogs [0] that tipping is basically part of the income in the US. Is that still true? In the Netherlands we generally agree with Mr. Pink, minimum wage is higher here though (I think).