wipe(1) доставляет:
Be aware that harddisks are quite intelligent beasts those days. They transparently remap defective blocks. This means that the disk can keep an albeit corrupted (maybe slightly) but inaccessible and unerasable copy of some of your data. Modern disks are said to have about 100% transparent remapping capacity. You can have a look at recent discussions on Slashdot.
I hereby speculate that harddisks can use the spare remapping area to secretly make copies of your data. Rising totalitarianism makes this almost a certitude. It is quite straightforward to implement some simple filtering schemes that would copy potentially interesting data. Better, a harddisk can probably detect that a given file is being wiped, and silently make a copy of it, while wiping the original as instructed.
Recovering such data is probably easily done with secret IDE/SCSI commands. My guess is that there are agreements between harddisk manufacturers and government agencies. Well-funded mafia hackers should then be able to find those secret commands too.
Don't trust your harddisk. Encrypt all your data.
@zombieff: Воистину доставляет.