Hi Pierre,
It really comes down to risk management (which are two very short words for a very thought-provoking area).
Just a couple of notes though ...
Data saved in a fire safe is at risk. Many confuse a fire safe with a data safe; put coins, notes, and typical backup media (hard drive - tapes etc) into a fire safe - let it burn to its one or 2 hour rating - and your money will be just fine, but chances are your data will be toast. Money and documents can withstand much higher temperatures.
Ideally, you really want to have your data stored at a safe remote location. A good example is Christchurch -- one of my country's biggest cities - about 400km from where I live - and it suffered MAJOR damage via a series of earthquakes. I'm sure that many had their data stored in safes - and a year later they still can't get to it (and who knows if it's intact); many of the buildings are in the red zone and folks still can't get in to rescue their data.
For what it's worth, my personal reigme is ...
- Data normally resides on a RAID 1 mirror pair on my primary PC - so if one of the 2 drives fails (and it's happened) then I lose exactly - nothing.
- Commerical projects (my landscapes for sale - studio & location shoots for paying customers) are written to 2 DVDs - one stored at the studio - one stored at home (I used one just the other day when I sold a canvas print - went to open the file to print another one - and found that it had been corrupted. Pulled out the DVD - restored - in business again.
- I keep work-in-progress on a portable solid-state hard drive - which travels between home and work with me
- Fairly recent copies of the SSD drive contents are mirrored on my home PC
- I upload a copy of projects to MediaFire.com (not a guaranteed backup service, but I'm happy to live with that).
- I also backup my systems to an external HDD
So up to 8 copies of the data are floating around at work - home - on the net.
In your case - you choose not to backup OS files - that's understandable. I do back them up, but having just said that - I really don't care too much if they're recoverable or not. Having just said THAT, having things like printer profiles backed up saves time (just learned that the hard way).
In your case, you might like to consider a set-and-forget automatic internet backup?
Just some rambling thoughts - no right or wrong - just degrees of safety.