First of all, I have not read through all of the posts here, and I apologize if this has already been mentioned...
What really gets me is when little envelopes are left in one's room - presumably by housekeeping services. I am not cheap and have no issue passing out a gratuity when I feel it is warrented - however when a gratuity is being "suggested" or even "hinted", it totally turns me off. We went on a cruise (Caribbean cruise line) for our honeymoon, with ports of call in Mexico, Ocho Rios (? sp), and Jamiaca, and I was appallled at how blatent the islanders there were asking for tips. We went on one of those tours - a boat ride to "swim" with sea rays. It was supposed to include the ride, snorkle equipment, and some type of rum punch as a beverage. Of course we are on the boat and half-way to the sand bar when the tour guides inform everyone that there will be no rum punch, but we can purchase beverages from their cooler (at inflated prices, naturally). Whatever - I could have cared less about the punch - but why advertise it when they do not provide it. It was not as though the tour was a "surprise" that they did not know they had booked. Then as we were all getting off the boat, the 3 "guides" actually make a big speech about how much fun everyone must have had, and how we shoud all "remember our tour guides" with a gratuity, also to those who did not know the meaning of the word "gratuity" - it is money! What a joke! It was far from free to take the tour, and it turned me off as we were getting off of the boat and the guides actually held out cans for tips. How pathetic. I would have walked right by but DH put something in their can.

If I had the time and a pen and paper, I would have wrote a note telling them how tacky they were and that would have been their tip.
Then in Jamaica, some dude at a "take a tour at some waterfall" thing offered to take a picture of us with our own camera - and after I complied, he actually held his hand out for a "tip" before he would give us back the camera! That was it for me - I did not so much as even look at another islander after that. I figured even looking may have costed me a tip. Never again.
As far as the cruise - sure, we tipped as I was told it is customary, however I feel the gratuity on a cruise ship should just be added into the cost of the trip, and then be done with it. For housekeepers - it really depends. We are not messy people and I always leave the room neat prior to leaving. If we made more than a normal amount of disarray, I may leave something for a housekeeper who had to clean up a little more than the norm. DH and I stayed 1 night at a B&B in CT last winter, and the Inn Keeper was the owner. It was a small place and he was the owner, cooked the breakfast (that was FAR from gourmet), and also did the cleaning - and there was still an envelope left in the room! It's my impression that a tip is not neccessary to the owner of a buisness. Please, correct me if I am wrong. Again my DH left something in the envelope (he is WAY softer than I am), but I thought it was ridiculous to suggest a gratuity.
The tip can and Dunkin Donuts is also a joke. The price of a hot (or iced) coffee is expensive enough. I worked at a coffee/donut joint when I was 15 and we could not accept tips - which was fine with me. Back then, I was thrilled to be getting minimum wage as it at least put a little cash in my pocket. What got me was when a customer insisted on leaving a tip (basically the change that was left on the counter), we had to add it to the drawer so the owner could keep it. HA, I suppose that is how the rich get richer, and the poor just work harder to survive, LOL. In my area of the world, there are now quite a few D&D's that have signs posted stating that tipping is not allowed - now that is my kind of coffee shop.
I think my new tipping policy just may be - if a service worker actually tells me that tips are allowed, I will inform them that I do not provide a gratuity to those who feel the need to suggest to me that is it accepted. Maybe that will open a few eyes.
I work in the medical field and my patients are my "customers", so to speak. I take all of their complaints very seriously and with the same compassion that I would offer to my own family member. That being said, I do not take tips, or gifts, or any other gratuity for that matter. To me, a smile or a "thank you" is worth its weight in gold. Everyone works hard for their money, and unless a service is truly a "gratuity-based" service, tipping should not be expected. Sure, I suppose I make a more proliferative income than a minimum wage worker, however I also put myself through college to be able to make a decent wage. I also worked at a ice cream shop and in retail, and took pride in my "jobs" whatever they were. No monetary tips were ever expected.
Okay, that's my comment on tipping, FWIW.