cos backing up would be a painfully slow,, as I have my OS,apps and docs on a 90gb ssd and all my other rubbish on a 640gb hdd. So when I backup my main OS ssd every few weeks, it backs up nice and fast, cos atm Im only 29gb full. My 640gb doesn't change much so dont have to back it up that often.
But thinking about getting a 2 - 3tb drive in the near future to replace my 1tb hdd that stores my shared media around the house as Im almost out of space
I did think about buying a NAS for my shared hdd, but it would use more power in the long run, as I dont have my pc on 24/7, only when needed, and I got the other computers to turn on my main pc automatically when needed to access my shared drive.