What is interesting to me is how indiscriminatly we are expected to tip these days. I see "tip buckets" popping up in odd places.. the dunkin doughnuts counter, the dry cleaner, I even saw a gas money jar for staff in a local bookstore.
What amazes me is there are situations where you are forced to tip despite the service, and others where service was excellent and there is not an opportunity, or there is a company policy against it (like the grocery store where i bagged as a boy)
I do not try to base my tip based on what i think the person is making. I have tipped well to a bartender who makes $700 a night, but dammit the guy was awesome and the service phenominal. I was alone with a van driver one day going to JFK, young guy fresh off the boat, loving life for his opportunity to be here, his attitude was infectious and his professionalism showed. He got $5 from me.
I will not, however, subsidize lackluster service by feeling obligated to tip a percentage regardless of the result. Rudeness, apathy, incompetence and unprofessionalism will not be rewarded, no matter how small the expected tip.