[stcredzero]

How can the user be sure that a program won't cause data loss?

An easy way to do it: never delete anything. This isn't too different than my OS X setup at home with Time Machine. I have exceptions set up for things like my VirtualBox images and movies. A more advanced system that can keep deltas of binary data would be even better. A solution designed for the clueless end-user would have some sort of function that would automatically keep less frequent backups for larger files.

Run out of room? The salesperson talks you into a hard-drive upgrade. HP, Dell, and Apple would be happy about this!

More accurately, never completely delete anything. The system would always keep around at least one version of everything. Yes, this would mean that secure delete is impossible, but this sort of system is for the casual home user. If you need secure delete, use a different system. If you are doing esoteric things with lots of large files, use a different system.

[briansmith]

That is very similar to what Windows Vista does with "Previous Versions", except "Previous Versions" automatically gets rid of old versions when disk space gets low.