Since it has been mentioned, there are places where tipping is not considered wonderful, and could even be considered a bit of a putdown. Some places it is cultural, and in a few it is enabled by strong labour laws requiring a living wage. In some places there is a "service charge" - sometimes it goes to the service staff, sometimes the entrepreneur's pocket - I usually inquire to determine what it actually means. (Don't you love the US proliferating room service fees, none of which goes to the delivery staff in most instances?)

In the US, people who are "expected" to be tipped often "enjoy" state laws that allow them to be paid significantly less than minimum wage, and some service people are at best marginally compensated (money and benefits.) As much as I enjoyed hernande's post, I don't recollect civil servants, public transit employees, commissioned salespeople, doctors and the like (or even airline pilots) being among them, however, so I don't worry about tipping them.

So, I tip accordingly, and guided by local custom - much along GDIW's guidelines. But not if the service is poor (I, instead of the lounge attendant, is bussing others' rubbish and dirty dishes, etc. or the hotel has hairs in the shower, etc. ) And IMO it is a great idea to leave the hotel maid tip under the pillow - it is CW that hotel staff vie for those tips, and will commonly resort to skullduggery to pirate them, like a bell staffer's snatch of your tip left in the bathroom whilst loading your luggage onto the cart.

You, of course, will do your thing - but since the OP asked, this is what I do...