I have the ContourGPS and love it. Can't comment from personal experience on the GoPro, but I couldn't bring myself to planting that thing on my Ski Helmet, prefer the profile of the Contour.
I also took the Contour on my bike to a track day recently and it work flawlessly.
Search the site, I posted the URLs in another thread. From the Contour site you'll be able to find my Ski videos as well.
Next stop is my moutain bike.
As for water sports....I guess I would need the water proof case, but so far that's not high on the list.