There is nothing more frustrating than a hard disk failure. And every HD fails at one point. It’s sure as death. However, there is a technology called S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology) that is built into most modern hard drives and it can give you early warning that you need to get your stuff moved to another disk. To check the SMART status of your HD you can open the Applications/Utilities/Disk Utility, click on your HD icon and check the last row on the bottom right. If it says Verified than you’re safe.
And if it says “failing” like mine, you better be scheduling a week of not having your Mac while it’s getting repaired.