Composition grayed out after installing NVIDIA driver in Squeeze
 

When you install Debian Squeeze from scratch on a new computer with an NVIDIA graphics adapter, the Nouveau driver is installed by default.

Nouveau doesn't work properly with KDE4. As soon as you open the Desktop dialog from System Settings, the Desktop applet crashes. (Which, looking on the bright side, saves you from being confused with any effects at all)

If you decide to install the NVIDIA driver from the Nvidia website in the Nvidia way, not the Debian way, you'll notice that the driver installs properly, but Deskop Effects are grayed out and cannot be enabled in any way. No error message or whatever.

The problem is that apparently some traces of earlier settings are present and not being cleaned up. The coarse solution is to remove ~/.kde. This is not usually a problem as you just made a fresh install and nothing is lost. A more fine-grained is to find out where this settings are stored, but the coarse method is faster.

During installation the Nvidia installer will complain that it could not disable the Nouveau driver despite a blacklist file being present in /etc/modprobe.d. Restart the computer (to get rid of any loaded modules or module dependencies and run the installer again. It'll work.

jlinkels