"Data that isn't backed up is data that you don't care about." ~ Quote I read somewhere.
But it is true. Hard drives may be expensive these days but they sure beat losing all your data. I bought a cheap ex-server hard drive from a computer shop, stuck it into my case, and use an extended power cable and only plug it in when I need to back up my stuff using
Allway Sync.
Of course it'll only protect against data loss or HD failure and not physical destruction or computer theft. Perhaps an external caddy or HD kept in a fireproof lockbox would be better.