A quick one:

If anyone is expericning ‘compositing not enabled’ issues with their applications on Ubuntu 11 – even though you have Compiz installed and it’s saying that Compositing IS enabled try this application below from Mariano Chavero.

http://marianochavero.wordpress.com/2011/04/20/a-simple-gui-for-unity-2d-settings-ubuntu-11-04/

This worked perfectly for me to re-enable compositing after upgrading to Natty Narwhal..