If you've not yet heard, Ubuntu will scrap X out-of-the-box and will use Wayland by default starting with the 11.x builds.
If you're not familiar with Wayland, read through
http://wayland.freedesktop.org/ . Wayland promises to be a faster alternative to X by going direct and scrapping some layers of the graphics stack. For the average user, this will not pose much of a problem. For devs, this will mean some tweaks into the code. But all in all, Ubuntu aims to be the first to have an even faster and more responsive graphical stack.