I found that if you are already running a very recent build of x.org and you already have working 3D acceleration then the rest of the changes are easily reversible.
I've got modular Gentoo 2006.0xorg 7.0 on my Mini-ITX boxen, but I'de be looking to try this on the bigger boxen which currently have SuSE 10.0 so probably xorg 6.8 (or earlier) on them.
It seems from the Ubuntu Forums that any of the following (or a combination thereof) will cause slightly more grief.
64bit distribution ATI graphics cards (there's a surprise) Dual head
So my Dual headed AMD-64 with Radeon X800GTO is probably not a good place to try it out !
if it really is anything other than "3D eye candy".
Erm, I'll get back to you on that...the Expose style switcher is a good plus for usability in my opinion and I could see how the transparency could be useful (although you need an additional transet package to make it really useful) but no...pretty much everything else is eye candy :-)
Ummmmmm .......
Peter