Try to think about everything on your computer right now. Think about the pictures of the kids when they were babies, think about all of the music you've amassed over the years, think about the home videos you've taken. Think about all of the documents you've created - like your tax information, important presentations for work and household finance information.
Now think about this. ALL HARD DRIVES FAIL.
My most recent post on Man of the House is also my diatribe on backing up your data. If I've cornered you at a party and given you this speech while drunk on wine, I apologize in advance.