There are two kinds of people:
Those who have lost data,
and those who will.A long time ago I wanted to digitize the collection of posters our church library had. I was the librarian at the time and it was frustrating to try and find a image for the Sunday School teachers to help out their lessons. Everyone knows that even a static image will help dramatically in knowledge retention.
There were a few thousand pictures and all I really needed was a thumbnail and the reference number. Someone had put reference numbers on the back and a slightly helpful catalog in a binder but unless you knew exactly which one it was it was a pain to find. I wanted something to be easier and faster to flip through.
So during class time and during the week I would take pictures of every image front and back until the cameras memory card was filled or the battery died. then I would type in the reference number, title and keywords in iPhoto. This part alone took a couple of months.
I was almost done, I uploaded the last batch of photos and then it happened. iPhoto crashed and the database was corrupted. While I had a backup of my family photos from before the project everything else was scrambled, badly. I was able to pick out our family photos but I gave up trying to reconstruct the project. A lot of work down the drain.
What would be lost if your computer's hard disk failed?
It isn't just family photos but many important documents and emails. Keeping them save is a bigger deal then ever before.
Nowadays, computers have backup software built-in, but have you turned it on?
The Mac has Time Machine and Windows 7 has Backup and Restore Center.
On the Mac if you just plug in an external drive it will ask if you want to use it as a Time Machine backup drive.
On Windows you'll have to tell it to use the disk but that is easy enough.
For more on keeping your Windows computer backed up and clean see this lifehacker post
But that is only the first level of keeping things backed up. The next level of backup is keeping a separate bootable backup. In case your computer goes completely belly-up you have a disk you can take to any other computer that you can boot from so it acts just like your old computer. For the Mac you can use Carbon Copy Cloner and for Windows Norton Ghost.
The next most important level is an off-site backup. If your home or office burned down having all the backups in the back room is not going to help, though a media safe would help (a regular fire safe gets to hot.)
This can be as simple as keeping a backup in your desk at work or at a relatives house. There are now also online backup companies, like Carbonite.
Now that your data is out of your direct control you may want to look into encryption, but don't forget to write down the password somewhere safe too. But that is another post.