X Window System is an old networking windowing system which almost all Unix and Linux graphical desktop follow.Recently Ubuntu dumped X Windows for Wayland, an OpenGL-based display Management system.It’s a display server for all Linux desktop and an associated protocols whose main function is compositing.
Last month Mark Shuttleworth sent over an email saying that they will be deploying in the Wayland Display Server with their Unity Desktop --thats replacing the GNOME shell by default -- in a future Ubuntu release! Just two days back Ubuntu 11.04 Natty Narhwal Alpha 1 got announced and the glimpse of Unity interface could be seen.However, the Wayland server deployment will not ship before 11.10 Alpha.
Adam Jackson on Fedora’s development list too showed interest on Wayland and stated
"Wayland's not a usable default yet. It'll probably be packaged in F15 [Fedora 15] as something you can play with. We don't even have a complete list of transition criteria yet, let alone a time-frame for switching the default. But it's likely to happen eventually because it's a serious win for a lot of things, and the downsides are pretty negligible despite the fear from the peanut gallery." Fedora 14 just came out. Fedora 15, which is the first version of Fedora that would include Wayland, is due out on May 10th 2011."
Whoever interested in understanding how Wayland is different from X should refer http://wayland.freedesktop.org/architecture.html