X has a warm place in my heart and has ever since I first logged into my high school's SGI workstation that students Weren't Supposed to Use. However, the multilayering approach encouraged/required by X is a vector for an awful lot of subtle bugs and UX inconsistencies.

I don't think it's the only thing holding The Year of the Linux Desktop back, but successful end-user systems all have monolithic graphical user environments, and [GNU/X/]Linux has this bric-a-brac tower of Babel. Attempts to rationalize the tower post-hoc, even with extreme prejudice like Gnome 3, are going to be less effective than building from the ground up IMHO.