Look at Apple, all busy filing patents and whatnot. Take this one (well, these ones), which shows several potential 3D interfaces for the Finder. The patents were first filed, according to AppleInsider, in June of last year under the name “Multi-Dimensional Desktop.”
It’s as you might imagine: the Dock & Co. are able to move along the Z axis in addition to the normal XY axes. A simple concept, yes—“hey, let’s make the Finder 3D”—but one that really hasn’t been deployed in any meaningful way yet.
The question then becomes, when can we expect such an interface? Probably not with the next version of OS X, 10.6, (that’s “O Ess Ten” not “O Ess Ecks”), or Snow Leopard, which is rumored to be released on next June. (Rumored in so far as Apple said in June that it was about a year away.)