I actually had a external HD fail on me one time and could not recover the data from it. I lost the data I had been backing up on it and within 1 week my laptop ( what I was backing up ) was stolen. All that data was gone and I had nothing to recover with.
With that ( and I know its rare/extreme case ), I actually use a few methods to backing up now. Right now I'm:
1. Backing up the most used/important files with dropbox
2. Doing a daily backup of all files to an external 2TB HD
3. Putting a copy of #2 and #1 on a desktop that ONLY is used for backups and nothing else and then this data gets IMG'd and sent to a cloud server.
I've got several laptops and desktops now ( all for diff uses ) and they all go thru the steps above. In case of fire, theft, failure, or just about anything.. I should be good to go.