I travel to the US fairly often, and I would like to make clear do always tip at the going rate.
However, it is a bit of a pain, due to having to have a constant supply of notes.
Also the thought that you could get screwed if the server doesn't like your tip, or if you don't tip for something you didn't realise was tippable, or you can never return to s restaurant if you leave a bad tip.
I would also like to point out that I think tipping is actually becoming less popular in the US in recent years. Could be something to do with the economy, I have heard a few America's complain about tipping recently, compared to absolutely zero in the late 90s / early 2000s. (As a Brit I don't dare for comment either way for fear of being assumed to be cheap, whatever I say)
Another anecdotal, I tipped $2 for a drink costing about $8 dollars a few years ago (my logic being it was like tipping $1 for a $3.50 beer in the late 90s), the bar tender was happy, and made a point of thanking me, we started chatting, as we had a few things in common, he said tips were way down and most people tip $1 per drink, whatever the drink.
RE: US server salaries, as a bar tender with tips in the late 90s in a major city, you could probably make 3 or 4 times the UK equivalent. I think it has probably gone down quite a lot since then, but I am sure most servers find the tipping system a lot more financially beneficial than the "civilised" uk system if they are working in a busy bar/ restaurant.