Gnome discovered (after shipping unfortunately) that spatial actually sucks rocks in general usage. The distros turned off spatial for one release, Nautilus backpedaled, and within 6 months everything was back the way it was.
I also submit Longhorn for your consideration. Microsoft explored and marketed all these exciting new technologies, then jettisoned them all before shipping Vista.
Let the Gnome guys play for now. Hopefully they hit on some really neat new features. And hopefully the distros will paper over their mistakes.