They're a good, cheap and almost 'disposable' HD rig.
Terrible for an underwater footage (ie: diving) but great for watersports.
They do use a rolling shutter with can seriously distort the image at times but on a whole the quality is great and they are tough little units.
I'm pretty sure a new version is out or coming out soon. Big improvement over the coming GP HD and still real cheap.
Oh and dawnpatrol, thanks for that link!
I use to do videography for a living a few years ago and have intentions of moving those skills into the water. Always racked my brain as to how I could get real cool shots that made my footage stand out above the rest...I had an idea about doing a 'bullet time' rig for surfing after seeing it used in a rally video with a bunch of GPHDs mounted on the back of a car. Looks like I was beaten to the idea...not like I ever would have done it or made it work anywhere near as good.
That is some seriously cool footage. Still...I love the simple old clips in Jack Johnson's surf movies all shot on old bolex 16mm film cameras