I would much rather not wear a helmet, but here are the reasons why I do...
1. 2 head concussions neither of which happened in the park. 1 was caused by an out of control skier and I was wearing a helmet. I still rode the rest of the day, but literally could not piece together a sentence and had a gnarly headache.
2. I like to ride through the trees...I'm guessing my head is not going to win of I hit a tree at speed
3. Double black diamonds with exposed rocks...in the even that I bite it, I would rather not tomohawk head first into a patch of them wearing a beenie...then again, even a helmet might not save me.
My main factor for wearing though, in all honesty is because I have kiddos and I'd hate for a nasty accident to take me out of their lives.