I've seen this before. For Law enforcment, it's actually a good tool, and probably about the only way to handle certain situations.
Nowadays, more and more people with something to hide will use some sort of hard drive encryption, which requires a passphrase when the machine is started. If the machine is powered off, the passphrase is lost.
Without the passphrase, there is no possible way to decrypt the drive, short of guessing the passphrase, which could take a very long time, (up to a few billion years) depending on how many characters were used...
