My wife got a new laptop and I gleefully offered to blow away the hard drive on her old one. This is the ultimate digital purge!
In the old days, the most dangerous command you could give your computer was: Format C:\
Ah, so innocent, weren't we? We had no clue that data could be recovered from hard drives after such a catastrophe. The simple truth was revealed to us when Peter Norton released his Norton Utilities.
In light of the revelation, the next logical utility class was DeleteShitForReal. My current favorite is Eraser, an open source utility. Hard drives won't know what hit 'em!