Hmm....the cube desktop didn't work for me (the fire effect did though). Then again I had an ATI card back then, and ATI + Linux = failz0r, plus it was VirtualBox v2. Heck even Cairo Dock was lagging. I've yet to try it on my Nvidia card with the latest version of VB though, expecting a lot of improvements.
KDE still sucks on VB though, I download Kubuntu 9.10 and ran it on VB to find that the pixels would get all messed up at the loading screen oO