in the states.... i consider 15% is what you give when the service sucks. For good service it should be at least 18%. And if you're in a large group, even sucky service should get that.
Okay, I am about to make my self TERRIBLY unpopular, but I thoroughly have to disagree with you here. Isn't a tip supposed to be a reward for good service? How on earth did we get away from that? (Yes, I know that for whatever bizzarro reason, it's now pretty much the norm for a business to pay it's employees jack, and expect them to grovel the rest of their wage from customers. If a restaurant considers serving food to tables part of it's business model, it should treat servers as regular employees. And if you know you have terrible people skills, and are incapable of being a good server, then perhaps another line of employment would better suit you).
If I get decent service (no complaints, but nothing notable), I'll leave 15%. I consider this doing your job. If you want more, go out of your way a little.
If I get great service (which means that no matter what went wrong, the waitstaff genuinely apologetic and tried their best), I am very generous, usually beginning at 25-30%.
And when the waitstaff can't even muster so much as a "Gee, I'm sorry it took half an hour for me to drag myself away from the pile of cute college students over there to come get your drink order, and oops, I screwed up all the dishes because I was busy fluffing my cleavage and checking out the bartender the whole time you were ordering because I have the attention span of a gnat's peter"; then they get crap.
I am sorry that the restaurant won't pay them a real wage, but you can't be a crappy waitperson, and then get mad that your customers didn't tip.
And NO, I'm not saying the OP was crappy, she sounded lovely. I'm referring to the quote above.