I've got Xgl running by following the instructions here. I've been waiting quite a while for somebody to provide an easy and non destructive way of installing Xgl. I have previously tried using Aiglx, but that didn't seem as stable; blurry fonts and X server hangs when switching between virtual consoles.
Xgl works very well on my desktop (P4 2.8, 1 GB Ram, nVidia fx5700 256MB) with the nVidia driver, but not so well on my laptop (P4 2.4, 1 GB Ram, ATI 340M IGP). As ATI haven't released a linux driver for the 320/340 IGP series I have to use the open source 'radeon' driver which doesn't yet support the pixel-buffer required by Xgl. As a result some of the effects are rendered in software, and some graphical glitches are visible.
To view/modify the shortcut keys for compiz (which provides all the cool effects) you'll need to run 'gconf-editor' and look at 'apps/compiz'.