Tipping Point

My wife said she was intrigued to find out that "they don't tip in Italy." The question of who "they" are and who "we" are starts to get a little blurred here, but pronoun trouble aside, we discover that it is a widely held belief that leaving a gratuity is unnecessary in certain parts of the world. Italy would be one of those places, if you are to believe the Internet posted wisdom of world travelers. Then again, some have suggested that though it is not required, it is encouraged, especially when service is exceptional. This is a little confusing, since I thought that was the purpose of tipping in the first place.
Or not. I am generally a pretty soft touch when it comes to leaving a tip. I have, on occasion, been overly generous or comparatively stingy in my own gratuitousness. This has been primarily because of poor math skills and lack of concentration at that moment of truth: putting an amount on that little line or laying down the proper number of bills and coins. Math is hard. The principles of tipping are not. Leaving an extra bit of money as a reward for someone doing you a service is completely accepted in certain countries and many venues. Before I got married, I never tipped a Skycap because I was pretty much a one-bag-carry-on-customer. I wasn't in the habit of tipping maids in hotels because I didn't ever see them. They were simply part of the door hanger signaling system for which I had specific focus on the "Do Not Disturb" part.
And yes, part of me was consumed with the notion of just who deserves a tip and who does not. Waitrons do. Maids and hair stylists do. Generally speaking, if someone is touching you or your stuff, you probably want to tip them. But I don't tip my dentist. He's got his hands in my mouth and I trust him with all of my teeth and that he washed before he set about poking and prodding. But I don't leave a couple bucks on the instrument tray on the way out. I tip the guy who parks my car at a fancy restaurant, but I don't push a five in the hand of the kid who hands me my burger and fries. Maybe I should, considering the kind of business I do with kids who hand me burgers and fries.
It's what I wonder about: Who deserves to put a tip jar on their counter? On their desk? At their work station? But don't ask Mr. Pink. We already know how he feels about the subject.