I don't know how universally true this is, but servers and bartenders I've been friends with have told me that their most consistently generous tips come from people who are clearly working class or also in the food service business. I guess they know what it's like. One of my best friends told me once that he'd rather have a whole evening of working-class people at his tables then a couple tables of very rich people, because while the rich people might tip him extremely generously, they might tip him almost nothing because they took offense at some minor misstep.

You know, I ate out constantly for the 5 years I lived in Germany, where tipping is not customary except for maybe a bit of pocket change as a nice gesture. I can't remember ever having less than excellent table service.