So we've done the legwork for you, talking with concierges, tourist boards, and other travelers to find out the real protocol on when (and when not) to reach into your wallet and how much of a tip you should give to waiters, sky caps, maids, doormen, and cabbies all over the world.

CNN: How to tip outside the States

The Guardian worries that such massive decisions are beyond today's eaters: "among diners, there are worries that ambiguity over what tip is appropriate could lead to an awkward post-prandial battle of wills between waiters and diners".

ECONOMIST: Business travel