I've had my GoPro pop loose from my board a few times and I've heard that it happens frequently. The mount can come off and the plastic housing that attaches to the mount can easily break. I've had both of these happen. I always leash it to something other than the mount (footstrap if its on my board or strap if its on my helmet), but if the housing happens to crack where the leash is attached to the GP, you're screwed anyway. luckily, this hasn't happened to me yet. If you get another one, there are a couple of companies that make what is essentially a life jacket for GP, so it will float. here's one:
http://camfloat.wordpress.com/author/camfloat/ also, i've seen a pretty sturdy board mount that screws to your fin mount and has a body that surrounds the gopro so it can't break off
http://jupiterkiteboarding.com/store/kite-hero-twin-mount-gopro-cameras-p-3028.html I don't have either of these, mostly becasue i've been too lazy to order them, but both items look like they'd help with not losing the GP.