I disagree with a lot of the comments here, but let me just say one thing:
Linux's failure to dominate the desktop market is multifolded. First, there is the lack of marketing effort behind it. Second, there is confusion with so many UI's that it doesn't have a defined look to the product. Third, is the lack of apps that people have come to rely on and are aware of. Fourth, after all the crapware companies put on their systems, Windows is actually cheaper than Linux. Fifth, most people use the OS that come installed on the computer they buy. They don't upgrade very often, and sometimes buy a new computer when their old one begins acting up. Sixth, the users and developers have both underestimated the competition. Seven, there is a complete lack of cohesiveness as different distros try to move in different directions. Eight, there is a complete lack of resources to move Linux forward enough to truly compete because of all the competing idealisms between distros. Ninth...
Linux has a lot of problems when it comes to public perception and whey it hasn't caught on. The developers and many of the users have simply had tunnel vision and haven't been able to see opportunity and take advantage. Linux is destined to be another BeOS, with Google's push of Android and ChromeOS, and Apple's success. People have found an alternative, and though some may be Linux powered, it's not Linux.
