All the cool kids are doing it... why aren't you?
I'm seriously impressed... I've got Xgl and Compiz running on my laptop (an i810 graphics chipset) and it all runs fairly speedily. The battery hit seems to be negligible (surprisingly) and as a result I get all sorts of cool goodies.
The coolest is Expose -- hit F12 and see all of the open windows tiled on your desktop. This has been available for MacOS X for some time now. ALT+TAB has a fancy new dialogue, which is good eyecandy but also handy for finding the window you're looking for. Windows now "burst" onto the screen and wibble-wobble when you move them about.
There are a whole bunch more plugins that I haven't got working yet -- one of the coolest is the rotating cube desktop... but this still seems fairly elusive for most people.
Great work Dave Reveman!