Projects at work go to back into CVS at least daily (it's part of the 'time to go home now' pattern). Things that are in a serious state of flux can get saved more frequently. (My current record is 19 minutes between CVS commits; the User changed their minds about the 'required functionality' four times between the second morning coffee and noon, a span of 90 minutes or so.)
in reply to I backup my files:
Non-work projects live on a portable hard-drive (Blessings on Seagate for the 5Gig flying saucer). I zip the entire drive and copy the archive to a RAID every Saturday afternoon. I have been burned once, so I get to be paranoid about my backups.
I Go Back to Sleep, Now.