I think Linux on the desktop hit its peak in the early 2000s, when 'Windows, Mac and Linux' was in people's minds, we had Linux companies like Loki and Transgaming etc, commercial games from Epic and ID, proper UX-focused companies like Eazel and Ximian, etc.
I think most people have given up, but that's OK: Linux on the desktop, back then, still made a huge difference to today. GNOME had GTKHTML which spawned a rival KHTML which became Webkit which now seems to be the app platform for the thing that came after the desktop - the browser.
Now I have more apps open in Chrome right now than I do in the dock, taskbar, gnome panel. So do many users. And the direction is more in the browser than ever.
It's not just Linux: worrying about the desktop per se is irrelevant - like worrying about the dominant groupware platform or the dominant LAN manager. OS/2 might be better than NT, but nobody cares anymore.