I wore a helmet for years, but recently stopped, after I read the best available research that I could find: 95% of bicyclists who are killed, are killed by collisions with cars going faster than 35 mph. In those instances, a piece of styrofoam on your head won't help much. There is no credible evidence that a helmet prevents any but the most minor injuries, injuries that one can easily fully recover from WITHOUT a helmet. Might as well be comfortable. Most of the other 5% of fatalities are MTB accidents, or those of high-speed racers, or people who die from other causes while they hapen to be on a bike (i.e., heart attacks). As far as I can tell, there are NO studies done that stand up to scientific scrutiny that demonstrate that bicycle helmets do any significant good at all. (That Group Health study in Seattle, on which some bike helmet laws are based, was laughable, from a scientific point of view.) In my own experience, as a commuter going 15-25mph, I have NEVER crashed on the road, I've only crashed while MTB-ing, in which case a helmet is entirely necessary. If you're going to the library or to the office on a paved road, helmets are superfluous, and a pain in the a**.