my daughter and son in law both work in "service industries"--she's a beautician, he's a busser and go-fer at a huge pub downtown (five serving areas). neither gets paid a living wage, as such. they depend on tips to make it, week to week. so, i've gone to tipping 20-25% across the board, unless the service really stinks, or they have erred in a big way. (interesting that in new zealand, it is considered an insult to leave a tip in an eating establishment-- "after all, we pay our workers a good wage. they don't require extra.")