I played with Compiz last evening. Had a lot of fun, customized it slightly, and was slightly amazed that it worked so smoothly, with so little work to set it up.
When I went to bed, I just locked the screen, as I always do. On Ultimate, I clicky the top right icon, looks like a door knocker I guess, then select "Lock Screen".
When I got out of bed, my screen was a black nothing. Clicking the mouse did nothing, moving the mouse did nothing, banging on various key combinations got me nowhere. I did the only sensible thing a guy could do under the circumstances - rocked the switch on the top left rear corner of the computer.
On reboot, I had lost the Compiz settings that I had made, but nothing else.
So - how does one lock the screen when running Compiz, and how is the screen properly unlocked? It would seem that after enabling the Compiz Window manager, using the Ultimate Edition default logout menu is a no-no, but I don't find any other options on the desktop.