There is no shortage of stories here on TUAW (and elsewhere) that extol the benefits of backing up your data. Apple even makes it ridiculously easy to do so -- with Mac OS X 10.5, Time Machine, a blank drive, and some spare time, you're set.
Nevertheless, despite your best efforts, there are unforeseen circumstances where you might need to utter those dreaded words: "I need to send this for data recovery." Perhaps your airplane landed in the Hudson river, and your waterlogged laptop was stuck with your luggage. Perhaps an external disk is suffering from a manufacturing defect. Perhaps your backup disk is the disk that failed.
Unfortunately, there is no way to sugar-coat this: Data recovery is a painful, patience-trying, and absurdly expensive process. But if it's the only way to recover mission-critical data, it could be your only option.
It was for me.