From what I've seen, GoPro is a fine camera, that is excellent at what it does. For me though, it isn't worth the $300-$500 price tag.
I just take videos while on my bike, mainly when on trips, and then post some of them on Facebook for family/friends to see, or maybe post here.
I got my Contour +2's for under $200 each, and am happy with their results. If I was a serious videographer, or someone in the business of making action videos, then I'm certain I would get them. For what little I do with them, it just doesn't seem justifiable. YMMV