So it's an everyday thing... people don't want to turn off their computer while their going out to the toilet..., etc. So they hit "ALT+CTRL+L", and the GNOME-screensaver locks their Desktop. After they return they just type in their passwords, and the work could go on..OK!
BUT: There are usually problems:
NEW (today): http://gu1.aeroxteam.fr/2012/01/19/bypass-screensaver-locker-program-xorg-111-and-up/
So what is the most secure way to Lock the computer?