I say it's an IDE device to usb converter. This device can take any IDE powered device (cd/dvd rom, hdd) and have it connect to any computer with an usb (1 or 2.0) port.
Why is such a device which does exactly what an external cdrom drive so amazing? Well, aside from saving my arse by letting me fix the laptop loaned to me prior to going to Hong Kong, it's also a nifty piece of yay. You plug in a 200 gig hdd filled to the brim with whatever data you want (to keep this legal, think company install files, drivers, the like), and you can easily go from computer to computer installing it all!
OMG just the thought of running around with 200 gigs of anime to share with people (because I'm too stupid to set up a wifi lan) is making me giddy....your turn!