Old guys like me remember saving files to 8 1/2" floppy disks. You always had to save a file twice, on two different disks, so that if one disk went bad (and floppies went bad with discouraging regularity), you could retrieve the data from the other.
Of course, hard drives came along. These were much more rugged than floppies, and didn't fail all that often. And people got out of the habit of backing up files.
But hard drives do fail. Not often, but it only takes once. And that's worse than a failed floppy, which might have only held 10 files. If you don't back up, everything is lost.
I recently got a question about saving files from a student whose hard drive failed. And I had to tell him there was little I can do.
So, even if hard drive failures are rare, it's vital to back up data in the off chance that you have one.
In the past, I have mentioned Mozy. It's a simple way to automatically back up your data. The free version has limited storage, but it's plenty for your papers and other documents.
If you want back up pictures, use Picasa or flickr or another online picture sharing service (some come with your digital camera). When you upload pictures to share, you are also backing them up, so you win in two ways.
And to be even safe, put your most important file on some additional service. We saw this week how Ruckus collapsed; the same thing can happen to the place where you're storing your data. If Mozy goes under, you can use another option. I've been trying out Mediafire, but there are many other free file hosting services.
It's best to prepare, so if the worst happens, you can recover as much as possible.