I'm glad I haven't read this thread, but I'll just throw in a bit of food for thought (HAR HAR). The way I see it, is that tip bottom line % is more based on the type of establishment you're visiting. If you're at Denny's or iHop, the average tip % at a place like that is probably 11-12%, obviously depending on many factors. A midscale place, like a Chili's or Applebees or a pub type place, I'd say servers probably expect and perform at the 15% range. The places I've worked more recently in my career (after almost 8 years of experience in my field), where you usually eat no less than 3 courses and your server constantly makes sure your wine glass is at its sweet spot of fullness, 18% should be the baseline. Of course this is all dependent on the individual experience but I've worked from everywhere from an all-you-can-eat spaghetti joint to the third best restaurant in the city, and this is what my experience tells me. Of course, I'm such a gem in my field that I scoff at 20% or less, but I can tell you no one's ever tipped me more than they wanted to out of obligation to the standards, but tipped me more because my level of service is often higher than they've experienced.
Regardless, if you go out to eat you need to budget your tip in there and not set your server up to fail just because you don't want to pay. If restaurants actually had to pay their employees a living wage you'd be paying stupid, stupid money to go out to eat, as well as the effect it would have on staffing overall would be detrimental to your overall enjoyment.