I found this helpful question Replace xscreensaver With gnome-screensaver (Xubuntu) but the executable gnome-screensaver-preferences can't be found. So I'm not sure what to do, to get gnome-screensaver working correctly.
How do I configure it if that program isn't there?
I know that this is a very late reply but hopefully someone still finds it useful. Ubuntu 12.04 and newer releases have no configuration tool for Gnome's screensaver as it is more a screen blanker than an actual screensaver.
Gnome's developers are not willing to change this, so you may want revert back to xscreensaver, which has a graphical configuration tool. Please see this question if you need help with getting xscreensaver back.
Try opening Terminal (By pressing Control + Alt + 'T') and then typing in 'sudo apt-get remove gnome-screensaver gnome-screensaver-preferences xscreensaver' Then once it's finished, type 'sudo apt-get -f install'. Then try installing gnome-screensaver again. I am sure there is at least one or two third party programs that you could use to customize gnome-screensaver. You could also look in the program 'synaptic' and search for 'gnome-screensaver' and 'xscreensaver', then reinstall gnome-screensaver if required.
