I am curious about one thing: how do servers feel about customers who stiff on tips because of bad service?
For an average experience, I usually tip 15%. That's my average for neither a superperb job or a terrible job.
As someone who has been on both sides of the isle, I believe in tipping well for a job well done. The quicker you get my food or drinks, the less you screw up my order, the more attentive you are (without obnoxiously hovering) the more your tip increases. Being a great server or effective bartender is a skill, requiring excellent interpersonal skills and time management. I have no problem compensating well beyond 15% for an excellent job.
Inversely I have no moral qualms, however, not tipping for atrocious service. I have only not tipped whatsoever maybe 5 times in my life. You have to seriously fuck up for me to do that, but it is not beneath me to do so based on their service (or lack there of, really).
"Political correctness is tyranny with manners." -- Charlton Heston