You should be backing up the data you keep on your laptop in case of hardware failure, theft, or an unexpected cup of coffee on your keyboard. This bit of common computer sense has a bit more urgency if you own certain MacBooks sold in 2006 and 2007, since their hard drives may fail suddenly with no notice. Fortunately, Apple has a free repair program: but only until the computer is (at most) four years old, and only once your hard drive has already failed.
If you didn’t buy an AppleCare extended warranty, you can still get a hard drive replacement once yours fails until three years after purchase or August 15, 2010, whichever happens first.
And remember: back up your data, people. My computer is one of the affected models, and I am backing it up RIGHT NOW, just like I do every few days. Really!