I did some Googling the other day to find out how I can add a shortcut on my GNOME desktop that would lock the screen. This turned out to be a bit of a challenge but being the persistent person I am, I was able to find a solution.
Here is the command I associated with a short-cut on my GNOME desktop to lock the screen.
gnome-screensaver-command --lock
This works on Fedora 14 as well as Ubuntu 11.04. I expect this command to also work on any workstation running a GNOME desktop.