Yeah, they do, but the standard seems to have moved up (I just left a restaurant and my wife commented by 20% might be too low as that's now the minimum). I'd bet it's because restaurants started showing typical tips as 15%, 18%, and 20% (and I've seen 25%). Or maybe because people want to feel good about tipping?

Whatever it is , it worked on me - 18% is my minimum, although to be fair, I'm lazy, so I figure out 20% because the math is easy. If it's an expensive place or the service was bad, I do 20% on the whole number only since that's close enough to 18%. Good service, 20% on the whole thing. Free food/beer/good service, and it's 20% and I round up and add a buck.

But I'm also lucky to have a good job and no kids, so whatever. I have zero problem if someone tips 15% - the whole system is shitty because you can bust your ass at a Waffle House to make $4, or if you work at a seafood restaurant that has good beer and check on a table just once, you can come away with a $15 tip. It's not fair.