Harvard Economist and blogger Greg Mankiw points to a recent article in the NYTimes that suggests they may be on to something:
Examining the data, he found that when he wore his helmet, motorists passed by 8.5 centimeters (3.35 inches) closer than when his head was bare. He had increased his risk of an accident by donning safety gear.
Why? You might suspect that cyclists wearing helmets are more prone to take risks. But studies have found otherwise. The real answer, Walker theorizes, is that helmets change the behavior of drivers. Motorists regard a helmet as a signal that the cyclist is experienced and thus can be approached with less caution. “They see the helmet and think, Oh, there’s a serious, skilful person,” Walker says. “And you get hit.”
As tempting as it is to ride with the wind blowing through (what's left of) my hair, I suspect I'll be wearing a helmet for years to come. Have to set a good example for the kids.