AdventureRob: GoPro's biggest advantage was being first to market, and hence everyone wanting this sort of camera using them by now.
There is a few competitors here in Japan too. Notably JVC have one with a mini screen on the side so you can playback instantly too which looked very good.
I think GoPro's market share (of 100%!?) will start to decline if they don't start innovating and building upon their great start. I'm sure Panasonic, Sony & Canon will want a piece of the pie soon too all having a good rep with video.
they weren't the first to the market. they were first to have good video quality in the action camera market. And the first to really market the action cam.