Here's how I feel about tipping... I've waited tables and it's a shitty thankless job. The restaurant pays you shit, and you average about 10% of your food sales in tips. Then, you're expected to tip out the bar staff and the buss staff. Next, the govt assumes that you will walk out the door with at least 8% of your food sales in tips and they tax you accordingly and take those taxes out of the paltry pay check you get from your hourly wages.
That being said, I feel uncomfortable tipping below 15%. If I've gotten good service I tip 20%. Once or twice I might have tipped 10% for really lousy service.
When I was younger I worked at sandwich shoppes and pizza joints, and it appals me that someone doing that job would put out a tip jar. In fact, when I was doing those jobs people would try to put out those jars and I'd make them get rid of them. I never tip someone who's only doing the job they're getting paid to do, those assholes can go fuck themselves.
Now, when it comes to bartenders the tip can be your greatest friend, especially when it's really busy and it's hard to get a drink. (Think like penny beer nights and shit.) All you gotta do is throw down a huge tip with your first drink order, and you won't wait for a single drink after that. This works great if you're out with 5 or 6 people, just have each person pony up like five bucks, go order the first round, pay for the drinks, and make sure the bartender understands that they're gettig a 30 dollar tip and to keep an eye out for you. After a round or two you can have people from your party start going up to get drinks with you and the bartenders will recognize them and give them the insta service too. That way you won't have to be the designated drink getter all night.
When it comes to getting a tip from tattooing people my motto is, "never expected, always accepted."