Going over Defcon material I came upon Irongeek's presentation of teensy.

Source: http://www.irongeek.com/i.php?page=security/programmable-hid-usb-keystroke-dongle

In a nut shell, it is a programmable device that you can have it send keystrokes once it has been plugged in. It does not rely on USB autorun which we are all familiar with.

I made a video of a POC demonstrating it calling back to a Metasploit handler using Meterpreter as the payload:

http://www.vimeo.com/14090717

Just another nice tool to experiment with for pentesting needs.