Compiz is a step in the right direction, but human/computer interface could be much farther along.
I would like a "Desktop" to more closely resemble a 3d world of unparalleled graphical beauty, a la "Crysis", complete with lapping water, 3d sound, and instant VOIP interaction with any friend as a 3d avatar on this "Desktop" (automagically culling their availability to 3d chat via Pidgin, and any protocol in pidgin). Any application could be shared real time as a floating texture inside this 3d world, or run privately as a texture in the 3d world. Making an application into fullscreen is just a basic key press. There is also a way to instantly minimize all the applications into a virtual pile of pages on the ground in the 3d world, that can be restored at any time with the same keypress.
This infrastructure in place, any movie, video game, photo, document, program, or other file should be instantly shareable between all connected Pidgin partners graphically in the 3d world. Multiplayer games can be started and shared instantly as a texture in the 3d world, and with continued VOIP communication. For example both parties could automagically load an emulator (zsnes, mupen64plus, dolphin, pcsx, pcsx2), and then play simultaneously while chatting, with gamepads on opposite sides of the planet (with good enough bandwidth).
Video chat should also just be one key press away with any avatar near by. Any two avatars should be able to connect in any way easily, privately, with strong encryption, via p2p.