I've read quite a few times in this thread to make backups of your bitcoin wallet. But if I'm not completely wrong, then even stealing just the backup data results in losing all your bitcoins. So from a security perspective, better don't make backup copies!
Theft if not the only thing you have to secure against: you have to secure your wallet against data loss as well. If you don't make back-up copies, you disk may fail tomorrow, taking all of your bitcoin with it. If you do make backup copies, you disk may still fail tomorrow, but you would be able to recover you wallet from the back-ups.
For the paranoid: you don't
really have back-ups until they are verified and stored off-site (preferably encrypted).