Project Looking Glass - the 3D desktop for Ubuntu or SJD
Sun Java Desktop have just released Project Looking Glass the ultimate 3D desktop!
It even has its own Looking Glass blog.
Looking Glass requirements.
CPU
1.4 GHz or faster recommended
RAM
512MB recommended
Graphics Card
3D accelerated graphics card, with at least 32MB VRAM and driver support for OpenGL, version 1.3 or greater (LG3D may run with OpenGL 1.2, but 1.3 is highly recommended). 24bit display depth is required in order for the X11 integration work correctly.
You can install Looking Glass on *buntu or try the Looking Glass Live-CD.
Finally here are some Looking Glass tutorials.