Brooke R. Busse, over on her blog, tells the alarming story of what happened when her computer got fried and would not start up again.
Offsite storage is the key. For my backup system, I use two thumb drives. (I tend to call them jump drives, which shows how much Battlestar Galactica I watched.) At least one is always offsite. When I’ve done an evening’s worth of writing, I back that up onto one of the drives. The next day, I exchange it with the one that’s been stored offsite.
Of course, that means I have to keep track of which files from the previous day to rewrite on the drive I’ve just brought back, in addition to any more work I do. It becomes a habit, and so not arduous.
I’ll have to look into online backups, also.