What's an appropriate tip for a guide or porter?

Tipping of guides, porters, and other staff is a well established practice on Kilimanjaro. Camp and trek staff (especially porters) are often poorly paid, and rely on tips to feed their families. I was amazed at how hard the porters worked for thier money, and I felt they deserved every penny of their tips and more.

However, many trekkers find that distributing tips at the end of the trip is an awkward and uncomfortable time. They're not sure how much is an appropriate tip, nor how to distribute the tips among the guides, assistant guides, porters, cooks, etc.

What do you think are appropriate tipping guidelines for Kilimanjaro? How did you decide how much money to budget for tips? Let us know by submitting a comment below.