How You Can Clear Your Screen Saver Selection Without Going Into System > Preferences > Screen Saver And Locking Up Your System

1.In a terminal window run: gconf-editor
2.Navigate to apps > gnome-screensaver
3.Go down to: themes
4.Right click then select: Unset Key

Your screen saver will now be the "blank" default.

Note: you maybe able to find gconf-editor under Applications > System Tools > Configuration Editor. This just saves you opening a Terminal window.

Thanks to SteveDee for this tip!