Compiz and the Meta key in Emacs
When I switched back to OpenSolaris I wanted to use Compiz instead of Metacity to have at least some eye candy. After switching to Compiz I noticed that the Meta key is not working in Emacs. Since it worked in the "Normal Visual Effects" mode I was sure it's related to one of the Compiz plugins that was turned on by default in the "Custom" mode.
After some trial and error I found out that the "Group and Tab Windows" in the "Window Management" section is the bugger. It uses a couple of <Mod4> key bindings and one of them is <Mod4>x.
Disabling that plugin makes M-x work again in Emacs.