I generally tip pretty well, unless someone screws up big time - but that's happened like twice.
The situation in the UK is different, as our waiters get a minimum wage, but when you pay by card, it sometimes asks you to pay a 10% tip. And a lot of the time, the restaurant then takes this money to pay the waiting staffs wages. So I always decline and pay cash - that way they get it as a bonus.
Also, you're not expected to tip in fast food places or for takeout - only really sit-down restaurants, though people sometimes tip in bars and pubs.
The weird thing is though that most of the places I go I end up being friends with most of the people there, and you do know how much some shit affects them. One girl at my favorite restaurant was saying that people sometimes stiff them on their entire bill, which means it then comes out of their pocket. So sometimes they work an entire day just to break even, and that's shit.
Yesterday I was walking home a friend of mine that works in my local (pub) and it started pissing it down with rain, so I gave her my hoodie. That's better than a tip.