The Linux desktop never got killed! It never was really living. As long as Linux is not sold on computers, it will never spread. Maybe things change in the future, Canonical is doing an insanely great Job bringing Linux to the masses. But personally I think Linux will take of in new markets (China, Brazil, etc), not in allready established ones.

By the way, in my oppinion only a small fraction is buying Macs because of OS X, it's the Hardware. Design and Usability of Ubuntu is a lot better than OS X at the moment.