Yeah, I'm thinking that when in the park I'll wear one or I won't try any rails outside the park. On a normal run I'm not too worried about being run into or hitting any rocks so I'll stay free in that circumstance since I've never had any issues with trees or rocks - although the base of my board might tell ya different: gotta love those exposed rocks in the worst places, lol.
Interesting to hear the different responses, but I'm a bit shocked at the responses towards wearing a helmet. In my time ripping down double blacks at kicking horse, sunshine and castle mountain, I found that most riders didn't wear a helmet. Should note that I NEVER ventured into any park terrain areas so can't comment on that, but sounds like it's exactly opposite.
well when I freeride (basically all I do) I wear a helmet because you can still get whacked by trees and such. So yeah go with a helmet