Gary raised an interesting point, so I thought I would start the helmet rolling.
I wear helmets for biking and for skiing.
1. I took a fall on my bike this summer that knocked me unconscious (or I fainted and then fell, I have no pre-event memory at all).? I completely
**** my bike helmet all the way through the foam and the plastic for about 8 inches.? I was out about 15 minutes, and went along with the paramedics recommendation to go to the emergency room.? The head scan was completely negative, no damage at all.? My daughter-in-law, while training for the Marine Corps Marathon, got run over by a biker at 25mph and broke her collarbone.? She also hit her head due to the impact and suffered bruising and bleeding on the brain that was a concern for a while.? Having such an accident is a long shot, having a helmet on "just in case" is as wise as buying car insurance.? No one expects to have a car accident, but we all buy insurance just the same. (no, I am not advocating that runners wear helmets, but the two happened close together and the different results struck me.)? Other than needing to buy a new helmet, I wasn't injured.
2. I can't begin to count the number of times I have been hit in the helmet by other people's skis while walking, while riding shuttles from the parking lot, while walking to the lift from the hotel.
3. I have taken at least one memorable fall while skiing when I slipped on a patch of ice.? Usually I fall on my side, but this time I fell rearward with enough force that I remember my head bouncing.? No aftereffects whatsoever, not even a headache.
4. I use a SmartWool helmet beanie, and the helmet is always warmer than any stocking cap or anything else I have worn, and this is especially true if it is windy.? With newer helmets and the adjustable headbands, it is now very easy to make the helmet slightly larger or tighter based on the thickness of what you want to wear under the helmet, if anything.
5. I can't think of a single disadvantage of wearing a helmet.