It can record 1080 170ยบ video, 11Mpx stills and time-lapse at a selection of frame rates with a fixed focus fisheye lens. It comes supplied with various mounts and a waterproof housing.
As is the GoPro can't focus underwater but a variety of add on lenses and tweaked housing are available for around $120.
Being tiny and light the GoPro can be attached to helmets, wrist and chest straps, kites, RC models...just about anywhere you can imagine.
Here are a couple of my early videos.
The sealed housing seems to fog up in the sun quite easily. Dessicant tissue pads are available to prevent this.
