As a Brit who lived in the US for a while I found the whole tipping thing a bit strange. I also worked in a pub for six years so see it from the other side as well. On the whole I find the concept of people being nice to you just because they want a tip really distasteful. Even if they would have been nice anyway I always feel like it is being nice for something in return which just makes me feel awkward. Because of this I never went out to eat much when over there.
As an aside, my wife worked in a posh hotel in Kennbunkport in Maine with a snotty restaurant attached where because of wine bills etc. it was not unusual for a tables total bill to be over $1000. There were some waiters who could walk out with over a $1000 in tips and some very intelligent people worked there who had not ever bothered to go to college or university because of the tips. As an economist that seems a very poor allocation of resources. What do we want to encourage - more doctors, teachers and engineers or more waiters? I suppose if tips are supposed to make wages up to the minimum wage it is slightly different but still can't help feeling the whole thing is flawed.