I currently fix Linux related bugs in my spare time. I do this as I would truly like to see a Linux based desktop become mainstream in my lifetime.
I spend most of my time contributing to the Hundred Paper Cuts project as I believe this is where my limited time is best spent - https:/
Update: Sadly this project died long ago.
My ultimate personal goal would be to obtain a paid position where I could work on these improvements full time. If you or your company would like to hire me for this type of position please feel free to contact me.
Update: Yay, I got a job working on the Mesa OpenGL drivers for Linux :-P