I got the idea from AJSlye: http://forums.netrunner.com/showthread.php?tid=23720&pid=38394#pid38394
It copies/clones your OS (i.e. partition or whole hard drive). If something goofs up bad, you can restore the last cloned copy. So if you clone every month, the worst that can happen is that you go back a month, and only lose a month's worth of updates.
I personally backup my data partition a different way, so I just clonezilla my netrunner OS partition.