I'm so obsessive about backing up - especially WIPs - I shudder when I hear other people saying they don't.
I learned the wisdom of frequent backups many years ago, when working on my little Amstrad WP. I still have fond memories of that little beast, despite it having some of the most illogical and frustrating features. Like no key to zoom down to the end of a file. On a particularly long story I could lose the will to write by the time I scrolled down through the pages to get where I'd last left off.
And then it had this wonderful habit of only telling me that I had run out of memory to save when I tried to save the ten pages I'd just spent an hour writing. There were two options you could try after that - one of which would have saved the text - but in reality that one never worked and either way, no matter which option you chose, the story was consigned to oblivion.
LabRat