Your hard drive will fail! Listen, all hard drives fail eventually; it is just a matter of when. Add to that all of the threats to your data from virus, spyware, etc, and it becomes imperative that you backup your files. Most people have hundreds or thousands of personal photos that are irreplacable.
It's Your Data - It's Your Responsibility
Visit www.mozy.com for free/cheap on-line & off-site backup. Visit www.lacie.com for a simple external hard-drive backup solution. Using both of these solutions together makes for an inexpensive, easy, reliable backup plan.