yep, after a major hard disk failure last year i wanted some form of major back up system.
Having tapes/etc backing up daily wasn't good enough
I wanted a raid system, but i didn't want the raid system inside my PC (due to the fact i move my PC a lot (LANs and back) and also means i can remove it when we go on holiday or away for the weekend (fire or theft)
I have the same "My Documents" folder since they introduced it in Windows 95, So its approx 100 gig in size.
I use a Buffalo system (looks like this)
I use the USB one, not the CAT5 (this is due to way i like the security on it)
All PCs in our house My Documents folder have a link to this device (all with their own folders) with automatic back up working for them.
I am planning on getting a networked system later this year, but will be using it as well at the USB one.
Cant rate the Buffalo systems high enough, they have do the job they say and they give me a massive piece of mind that my data is secure.
Just to add, its the 500 gig x2 drives i have in mine.
So, my advise, yeah grab a Buffalo system, USB or CAT5 is down to your needs (or both)