The number 2 desktop OS, with 5% of the market, is Mac OS. The reason for this is 80% of Mac OS users don't care about the OS, they only care about the glamour Apple has created. Apple could be running Windows under the covers for all those people care.
Ubuntu is not going to conquer the desktop because it is a "better Linux" (unless the desktop goes away except for die hard Linux aficionados). The question is, is there a future for the desktop computer? Will it be replaced by the mobile device that plugs in to the big screen and links to bluetooth mouse and keyboard?
I just had an electrician in to replace a chandelier. He had a desktop computer, but it broke, and now that he has an iPhone, he sees no need to get his desktop fixed.