I think market share is important to the extent that the OS receives enough developer support to be easy to use. What I mean by easy to use is you can generally

I think market share is important to the extent that the OS receives enough developer support to be easy to use. What I mean by easy to use is you can generally find good software and you don't find it difficult being a user of a niche OS in a world where most people use something else. Linux on the desktop feels about the same as Mac OS X back in the early 2000's. It hasn't quite taken off yet, but it's past the point where you can be a user and generally expect things to work well. Overall, I'm very happy with where Linux on the desktop is these days.