Perhaps it's the implementation rather than the protocol that I should constructively criticise.

The implementation of X, used on Ubuntu for example, lacks professional touches. At times, when the system crashes or boots up, the title bar disappears off all the windows. Why does this happen? Also, there seems to be a lack of a de facto window manager. All these different window managers serve to just confuse. It's small things like that that need to be ironed out before Unix/Linux can become a true alternative to the more polished commercial Windows and OS X.