Widely used by professionals and hobbyists. The cameras have been used to film inside of the mouths of alligators, sharks and polar bears.
The company currently only sells three basic cameras, none of which in its native format have a viewfinder or zoom lens. The only menu is a 2-bit LCD that appears on the front of the camera and is cycled through by pressing combinations of the front button and a top shutter button.
The cameras have dimensions of 1.6” x 2.4” x 1.2” (42mm x 60mm x 30mm) (HERO2). Ranging from capturing stills at 5 to 12 megapixels. The cameras are bundled with a clear polycarbonate HD Housing (with glass lens) that is rated shockproof and waterproof to 180 ft/60 meters. The housing consists of a quick-release buckle on the top and threads at the bottom which can be used with a special screw to connect to all of the GoPro mounts.
The housing has metal buttons which are synched to connect to the camera's controls. The housing has a "skeleton" backdoor option to access the back controls and microphone in situations where it is not necessary for the camera to be water tight or shock proof (but wishing to take advantage of the mounts).
In addition to the usual camera features, the cameras also include an upside down mode to make the photo/video appear upright when played; interval shooting of every 2, 5, 10, 30 or 60 seconds allowing the camera to continuously shoot unattended; 3 photo burst; and self-timer. The camera spec sheet notes they have a proprietary 1050 mAh lithium-ion battery (HERO3), Aperture: f/2.8, and rated >1.4 V/lux-sec in video mode.
Source: Wikipedia, Facebook, GoPro