Ouch. I've had to start over from scratch before. It's not fun.
I recently backed up my fanfiction and graphics files. I do that once every couple of months or so. Geocities and ff.net also serve as backups for me.
I've been playing the Sims 2 game lately (and yes, I have Lois & Clark sims, lol). It's the saved characters I'd feel the most bad about losing.