New Scientist offers a list of the human body's five organs and functions that seem to be pretty much useless. (The appendix isn't on the list because recent research suggest it may actually be a "safe house" for helpful bacteria.) Making New Scientist's, er, cut of vestigial organs and functions are: vomeronasal organ, goose bumps, Darwin's point, tail bone, and wisdom teeth. From New Scientist:
Though goose bumps are a reflex rather than a permanent anatomical structure, they are widely considered to be vestigial in humans. The pilomotor reflex, to give them one of their technical names, occurs when the tiny muscle at the base of a hair follicle contracts, pulling the hair upright. In birds or mammals with feathers, fur or spines, this creates a layer of insulating warm air in a cold snap, or a reason for a predator to think twice before attacking. But human hair is so puny that it is incapable of either of these functions.
Goose bumps in humans may, however, have taken on a minor new role. Like flushing, another thermoregulatory mechanism, they have become linked with emotional responses – notably fear, rage or the pleasure, say, of listening to beautiful music. This could serve as a signal to others. It may also heighten emotional reactions: there is some evidence, for instance, that a music-induced frisson causes changes of activity in the brain that are associated with pleasure.