The gopro's are good, but I've heard from a lot Of people that they have bad battery life, especially in cold conditions. I looked at getting one, but they're expensive.
I made the compromise and my girlfriend got me a Veho Muvi Pro, with the waterproof case and other mounts, it's only $99 on amazon. Been recording things this week skiing and the quality isn't bad for the size, smaller than my thumb!
I'll take some shots from One of the bikes soon, just to see what the quality is like. Just my $.02. The gopro is HD though, which is nice.