I have found this an interesting thread to follow, but I'm not sure as someone without an axe to grind (someone looking for good answers), I've found much go on in terms of making a decision on the helmet or not.

I wear one while mountain biking, because due to my clumsiness, I have managed to bump the noggin' off of trees and rocks, and I'm happy I had a helmet.

I haven't worn one on my 3.5 mile commute, because this commuting thing has made me feel like a kid again, and in small town Texas I never wore a helmet and neither did anyone I knew. But in the late 70's early 80's I don't remember it being an issue. I'm pretty sure if they had been anywhere near popular, my overprotective (but sweet) mother would have forced me to wear one. As it is, I still have scars on my knees from those days, and I show them off proudly...oh, and definitely no head injuries.

Being back "into it" now, though, I do sometimes wonder. I've already been buzzed by SUV's going quite close and at what seemed to me to be a high rate of speed. If they or myself (afterall, we all make mistakes sometimes) mess up and I get clipped, would a helmet help me?

I think arguing "well you're safer biking rather than not biking and getting disease" is specious. Let's just agree that we all think biking is better than not biking.

Once you've gotten to that point, however, the question becomes "with or without a helmet?" And I'm not sure deaths are the only quantifiable measuring stick of the worthiness of a helmet. Concussions/head wounds are worthy of thought.

But if you tell me "hey, when a vehicle clips you at 30mph or more, it doesn't matter whether you have head gear on or not," then I'll accept that. Maybe.

It just seems like I've read 6 pages, and I'm not anymore clear on what course I should go in terms of safety and enjoyment combined than I was when I started.