I spend a fair amount of time discussing computer backup strategies in my Chapter III of my book. In case I ever thought I was preaching mostly to the choir, I was just reminded by an email from a stressed out colleague that most people still don't back up their data at all. When a computer crashes, those folks are helpless until a technician can attempt to recover their data and perform any other parts replacements or repairs. Sometimes the data can be recovered, and sometimes even with technical support, it's just plain gone because the hard disk in the computer has died.
Home computers often have hundreds of digital photos, email and contact information for friends and legal or financial information. Work computers not only contain corporate data, but often also house personal email account information and photos.
If you can't be bothered to learn how to back up critical files to an external USB port hard drive on a regular basis, then please do the research and purchase a continuous online backup program from a company such as Mozy or Carbonite. Given the amount of time each of us spends on the computer, it's worth it to eliminate at least one source of high anxiety when your computer crashes.