Have you ever used Linux at a deep level? As someone who regularly uses Linux, I can tell you that this system is FAR FAR away from being a viable alternative to Windows in the desktop market. It's not that the system is bad, but it is too complex and hasn't been polished for the average user. If you are a computer enthusiast, you run an older machine, and you have spare time on your hands, Linux is fun to play with---and with enough patience it is a great replacement for Windows.

The closest thing we have right now is OS X, Apple's operating system based off of UNIX---the system that Linux attempts to clone. The Linux community needs a group that can make the system user-friendly, and until that happens, it will never be viable for the mainstream.