I've installed XGL and compiz-quinnstorm again. I'm somewhat disappointed. I was looking forward to a night of hacking and tweaking and getting things to work. But the darn thing installed with no problems at all. :( Even on my AMD 64-bit dual core. I thought I'd have trouble getting it to compile for amd64, but nope.
emerge layman layman -f layman -a portage-xgl emerge xgl compiz-quinnstorm gcompizthemer
That's about it. Though I had to unmask some packages and write a few shell scripts to make sure everything starts that needs to start. And now I have a bouncy, wobbly, semi-translucent desktop. mplayer works, zsnes works, and that's about all I care about. I'm using compiz in conjunction with KDE, and it works perfectly fine.
One great new thing about compiz is that you can use themes. There are already a huge amount of amazing themes made for it. Including the obligatory Mac and Vista ripoffs. I find it hilarious that I can use a Vista-themed 3d-accelerated Linux before Vista is actually released.