Wooden helmets might be a new concept for biking, but Jeff Snyder has been making and wearing them for whitewater padding for at least 15 years. Not sure how many he ever sold.
He's wearing one in this vid, and in the intro I think he might be wearing a wooden visor while unicycling. Jeff is the standup paddler with the blue inflatable.
http://www.youtube.com/watch?v=Mm7vHPPdkzI