Change Default Screensaver to XScreenSaver

I love the XScreenSaver but both Ubuntu and Linuxmint ship with the Gnome screen saver enabled by default.  This handy tutorial describes how to change the default screen saver to XScreenSaver: http://ubuntuforums.org/showthread.php?t=195557

As a sort of bonus it also describes how to install the extra screen savers in the repositories that don't come installed as default:

sudo apt-get install xscreensaver-data-extra xscreensaver-gl-extra