Not everyone's compelled to backflip across a canyon on a BMX bike or dive from suborbital space in search of extreme sports thrills. In fact, most of us armchair enthusiasts prefer to get our kicks secondhand. And, more often than not, that footage comes from the likes of a helmet-mounted GoPro camera. Action sports enthusiasts have been wearing these nearly "invisible cameras" (as GoPro calls them) since the company launched in 2004. It's proven to be a very a lucrative niche for founder and CEO Nick Woodman, too, considering the company's recent IPO filing pegged its valuation at $3.86 billion dollars.