I personally wear a helmet and I can think of a couple of occasions when it has spared me some stitches at the very least. That being said, I generally ride much more cautiously on the rare occasions I forget to wear a lid. Definite false sense of security.

I don't think anyone had mentioned this earlier, but it appears that in many cases, not wearing a helmet will provide you additional breathing room from drivers on the road:

"His findings, published in the March 2007 issue of Accident Analysis & Prevention, state that when Walker wore a helmet drivers typically drove an average of 3.35 inches closer to his bike than when his noggin wasn't covered. But, if he wore a wig of long, brown locks—appearing to be a woman from behind—he was granted 2.2 inches more room to ride. "
http://www.boingboing.net/2007/05/13...s-inspire.html

It appears that wearing a wig provides even greater benefit. Though, the only wig I own is of a filthy mullet.

I hate to open this can of worms, but do mullets work?