For some time Novell has been working on an opengl-enhanced X-server called Xgl. Few days ago the Kororaa project has announced a Gentoo-based livecd featuring Xgl. Currently nvidia and ati graphics card are supported via the “nvidia” and “fglrx” kernel modules. If you happen to own a supported graphics card you should definitely give that live-cd a try: I’ve tried it ony a Sony Vaio VGN-A217Z notebook and the effects were just great. Real transparency, wobbling windows, smooth desktop changes - it’s impressive what novell has built. There are videos on the novell Xgl website showing the effects but it’s even more impressive to try it out yourself.
The gentoo-wiki also has a detailed explanation on how to get Xgl running on Gentoo. Unfortunately my ATI Radeon Mobility 9200 doesn’t seem to work with Xgl yet.