Backing up things like "My Documents" to an external HD is great. But the problem is if you have a O/S melt down or a system drive failure, your going to have to reload windows, and the 200 or so updates PLUS all your programs like Office. Your also going to lose all your settings.
I would suggest your check out a disk image/cloning software like Norton Ghost to get a complete image of your computer for a worse case senario.
I agree but as a person who removes viruses for a living i worry about people backing up viruses, corrupt registry info, junk, etc when using a program like that