I’ve got a Dell Studio 1737 laptop, on which I dual-boot Windows 7 and Fedora 12. But with the default  graphics drivers installed by FC12, I’d receive an Accelerated Graphics Not Available error message if I tried to enable System > Preferences > Desktop Effects.

The solution was to do:

yum install mesa-dri-drivers-experimental

then log out and log back in (I didn’t even need to reboot).

Now I can enable Desktop Effects, including Compiz, which turns on Windows Wobble When Moved and Workspace on a Cube, the latter being the coolest thing to show off to your friends about a Linux desktop. Once enabled, just hold down CTRL+ALT and move the mouse arrow.