Comment 21 for bug 528094

Brian wrote in post #14: Also, if I run xscreensaver-command -lock it works correctly. Pressing <ctrl>-<alt>-L works but only because I added it in Compiz as a command, which runs xscreensaver-command -lock. Otherwise it did not work.

I believe that <control><alt><l> is Ubuntu's default lock-screen key-combination. It works for me (activates xscreensaver lock) and I have not added it as a custom command. Moreover, I'm using the default visual-effects.

I've just:
sudo apt-get install xscreensaver
sudo apt-get remove gnome-screensaver

Lucid x86-64