one of my old 'puters actually had a bit built into the usb controller, so you could run a usb cable to another 'puter and it would see it like a network adapter. it was a test mobo, so i don't know if the feature actually made it to market... but it was quite nifty
i agree that a nic is technically more suited to the job... but don't write off usb completely, for the less experenced user it's a godsend