Here's another good bicycling link from Bicycling Magazine.
"These are just a few of the examples of how modern helmets are far safer than those from even a decade ago. Further proof that helmets are safe: Don't wear one and you die. According to the Insurance Institute for Highway Safety (IIHS), since 1998 thousands of people have died in bicycle accidents, more than 90 percent of whom weren't wearing helmets. In 2008, IIHS stats show that 714 cyclists were killed. Only 58 of those cyclists were wearing helmets. The rest, 656, were lidless."
Bicycle Helmets: Injury Prevention | Bicycling Magazine