Description of problem: fast-user-switch-applet runs `gnome-screensaver-command --throttle` to blank the screen, but this is not a command that gnome-screensaver-command has. This can be seen by attaching strace to the fast-user-switch-applet process. Version-Release number of selected component (if applicable): fast-user-switch-applet-2.18.0-1.fc8 gnome-screensaver-2.19.1.1-1.fc8
Filed upstream: http://bugzilla.gnome.org/show_bug.cgi?id=477639
And fixed in rawhide now