So.. I write a quick script to resize the master images and re-generate around 2,000 thumbnails. Except... I copy/paste the source path to destination - and I mistype 200px width as 20. Now we have a whole site with long thin product images and no originals to recover from! As in the linked story, no backups were in place and all work was done on production. Lost a weeks wages over that, and had to manually re-add everything from a stack of CD's :)
Lesson learned? Don't let pressure force you into making bad decisions. I knew I really shouldn't be doing that but I was young & foolish.