You can follow the various threads here, here and here of the old "helmet discussion" Nemesis. I usually wear mine; the only time I don't is when I wheel up to the local plant nursery a mile away. That said, when the RCCS took our Paris-Redux ride back in April, one of our riders hit a puddle-filled hole going slightly downhill at speed. He catapulted over the bars and landed directly, and I mean DI-rectly on his helmet-ensconced head. Without it he would've been hurtin' for certain. If I have one of those days when I feel like going "free", I'll think back to that day and probably make the safer decision.