With the latest VirtualBox (I'm runing 2.2.2) you can use the Compiz 3D effects with Ubuntu 9.04 Jaunty. It doesn't run great, or even good, but it runs non-the-less. There is a lot of graphics corruption, especially at the top of the screen, and windows will have random graphics corruption. So even though it is not currently very usable, it is there and hopefully over time it will mature.
The screenshot here shows Cube Atlantis, and the second shows Cube Atlantis with the Desktop Cube, 3D Windows, and Cube Reflection and Deformation.