I can't see paying anything less than 20% unless I receive crappy service. If I can't afford it, I won't dine out. It's always a budgeted cost.
I live in a heavily touristed area and certain establishments that are known to attract Canadian tourists will tack the tip onto the bill because the servers often get shafted.
Good or bad, in the US, most servers are paid what amounts to a stipend. They get paid (tips) according to how well they've done their job. In very few places, they're paid well and great service is expected. But why it's done and if it's 'right' is an entirely different thread.
When traveling, following the local customs is the way to go. If you intend to revisit a particular establishment, you definitely want to be sure to tip well.
