Do you have a backup policy that covers the Worst Case Scenario?
I have one hard drive connected to my iMac for use with Time Machine. In addition to the Time Machine backup, I maintain a bootable clone of my iMac's hard drive using SuperDuper. The hard drive with the bootable backup is stored at my in-laws' house (you could just as easily store it at a friend's house or at work). The off-site clone is updated once a week.

With this setup, I can recover individual files from Time Machine if necessary, but I have an off-site backup in case of a catastrophe (fire, burglary, etc.). Some people maintain a much more redundant backup scheme, but I think this provides adequate protection with relatively little effort.