You can get a complete, multi-user, multi-purpose OS with top performance for free.
Please compare the speed at which the Linux kernel gets patches to the speed at which Adobe Flash gets patches, and you might understand why openness is important.
There are many places where Linux excels. There are also some where it does not -- like games. I wouldn't trade the advantages for a latest DRM-infested Blizzard borefest, which is where many new Linux users want to take it. Openness is important, but it carries certain costs. I can live with them.
1% of the desktop is fine. It's a really usable system. I can run scientific calculation on Linux running Octave, and it doesn't cost a thing. A single MATLAB license on a legal MS windows environment with all the needed extensions would be more expensive than our entire lab, including the robots.
I'm very happy that some zealots insisted on giving me an open alternative.