I don't have a GoPro, but I think it would be good for filming your friends surf. Could get some good barrel shots if you're paddling out or something.
The coolest footage ever (...lost it on a stolen laptop....) was when we clamped it on my friend's great dane's collar and let him "fight" his mastiff (no mike vick, these dogs live better than I do, they just play around a lot) but the video was effign terrifying.
go pros can be really fun. i love to use them on downhill bike to analyze lines on runs but for surfing, especially with the board mount, i think the footage looks weak/lame.
I think surfing animals are lame! I know its not a product, but its dumb. Saw some guy over seas with a damn lama on his board and thought the lama loved it.
carbon fiber surfboards
this is personal opinion but I'm gonna add beater type boards.
going off of your dog collar idea, i think it would be pretty neat if somoene mounted one to a sea turtle's shell & let it loose. i bet we'd learn a LOT about where they go & what they do from something like that! or someone could put one on mary lee as she cruises the coast!