At one of the first Southern Magic meetings I attended two years ago, a member had recently lost a lot of her work and reminded everyone to be sure to backup your work. Well, her exact words were, "Backup your damn work, people!" And that stuck with me. :-)
About every four hours I backup my WIP. I work in Scrivener on the Dropbox cloud, which saves every two seconds (literally), but I wanted more protection that that. My internet is not reliable in the country.
So, I compile my WIP and save it on the desktop and a thumb drive. Finally I email it from my Yahoo to my gmail accounts.
I had a small scare recently, which made me wonder if that was not frequent enough. So, tell me, how do you backup your work and how often? Does it depend on your word count or pages or time you've spent?