Next-generation Desktop Environment

surfing in the web I found this excellent and exciting video of a 3D desktop prototype. After many years of a poor bidimensional desktop, there is some attempts out of here: Sun’s Looking Glass Project, Xgl, the incoming Vista and other minor release.
In the meanwhile the UI was improved, see the Win3.x => WinXP step or the better KDE/GNOME environments, but probably a sprint in this way was given from MacOSX.
Only one question go through my mind: a really compless interface like that one in the video can be really usable?