[rez]

I think there is nothing more irksome than to spend over an hour on the computer cleaning up a cover scan only to have the 'puter freeze up and lose all the work.

That's all I'm going to say about it.

[Yoc]

or how about a blackout happening? 
I know how you feel.   

[OtherEric]

Ouch.  I don't do much cleanup on my scans other than cropping and rotating- I lack the tools and skills- but I feel your pain.

[JonTheScanner]

Make a copy of the original.  Work on the copy with frequent saves.  I've learned my lesson the hard way.

[Geo (R.I.P.)]

When I do heavy duty clean up on the cover scan, I try to save it every five minutes to be on the safe side.
I do feel your pain.

Geo

[John C]

I try not to give time-based advice about making backups.  It turns everybody into a paranoid clock-watcher.  Instead, I like to recommend that you save "anytime you do something interesting," under the assumption that you shouldn't waste your time redoing interesting things (or remembering how you did it the first time).

Sadly, what you'll never find in a thread like this is "how to keep the system from freezing."  Yeah.  Computers make us more efficient.  Riiiiight...