The Null Device
Jeroen of Spritesmods (who previously built a miniature arcade machine out of a Raspberry Pi) has an interesting piece on the possibilities of hacking the controllers in hard drives; most hard drives these days contain embedded ARM-based systems, often with reasonably powerful processors. (One WD hard drive had two ARM Feroceon cores, similar to ones used in network-attached storage appliances.) It is possible to reprogram the firmware in hard drive controllers, which has a number of defensive, offensive and other applications, from silently patching system files to insert exploits to detecting attempts at drive imaging (such as by police, customs officials or spies) and returning corrupted or falsified data. (I wonder whether algorithmically generating a FAT32 filesystem, empty except for one file named GOATSE.JPG, would be feasible within the memory footprint.) Also, given that broken hard drives with perfectly functional controllers are literally free (they're legally electronic waste that costs money to dispose of correctly), they could possibly serve as a source of free microcontrollers for various projects, such as hobby robots or circuit-bent musical instruments (assuming that one figures out how to make them control things other than hard drives).