How safe to upgrade - Backup first?

All,
I'm wanting to go from 0.3x to 0.4x but how safe is it?
My friend upgraded his from 0.3x > 0.3x and it completely ballsed his installation up and I'm a little concerned about going from one "major" version to another.

I know there isn't a "config backup" facility (why o why o why is there not?!?) so which files could I backup so that it gives me little headache should I need to reinstall. The last thing I want is for my disks to become unusable should i need to completely reinstall, let alone having to set all of the settings /plugins up again.

Cheers

well as i said, a friend updated and it completely went tits up for him and that was only upgrading from 0.3 to 0.3 minor releases.

I would feel a lot more comfortable if I had some kind of backup solution aspect to the OMV. Completely bemused as to why it doesnt already exist.