When using gdm (init 5) xscreensaver won't work. It also doesn't work after login as root and using the Gnome Control Center to change screen saver settings. I suspect this is a problem with X's security not allowing xscreensaver to run at the gdm login screen. Maybe it is a feature and not a bug. Robert
xscreensaver will not work as root. *** This bug has been marked as a duplicate of 10715 ***