I have had my hard drive fail. In fact I have had a lot of drives fail. This may be a shock to people but hard drives fail. They have moving parts and run at high speeds so they will fail. What frustrates me is how many people do not backup. There are so many tools that automate backups and make it easy. I suggest if you are reading this you should backup right now.
Here are some great free tools:
http://www.mediamax.com/home/xl.aspx
www.idrive.com