It's entirely possible that you may not have heard of Linux. Maybe you own a Mac or Windows computer and don't read the technology news. You may have a TiVo, but it doesn't have a huge sticker on the box that reads "Powered by Linux" (even though it is). You may use Google, but it doesn't have any announcement on its homepage that it's run on Linux servers (even though it is). Whether you've heard of Linux or not--it probably plays a role in your life somehow.
In all likelihood (yes, even if you're reading this), you probably don't have Linux running on your laptop computer at home or your desktop computer at work. The "desktop market" is dominated by Windows. Mac has a very small share of desktop computing (arguably even smaller than Linux's market share--it depends on whom you ask), but it is high profile--Apple stores abound in the US (there are also locations in the UK, Japan, and Canada), Mac computers feature prominently in Hollywood movies, iPods are the portable player of choice, iTunes dominates the digital download market, computer peripherals that are Mac-compatible have a logo on the side of the box indicating that they are, and major software is available for Mac OS X (Adobe Creative Suite and Microsoft Office, for example).
So why are you probably not running Linux on your computer? Why have you probably not even heard of Linux? What's stopping Linux from being more high profile, being more widely adopted?