In the post on backing up, I forgot to mention one crucial factor:
You must occasionally test your backups!
Every now and then, try to pull a file from your backups. Restore a couple of things you deleted a while back. Just to make sure everything is working. Computers are machines and machines fail — there is a chance your backup will become corrupt or otherwise borked. (One more reason to have multiple systems in place!) So, take a minute once a month or so and make sure everything is working. Odds are it is, but if not, better to catch it (and fix it) sooner rather than later.