Isn't it quite easy to block USB storage devices at the OS level? I mean hiding the stick is clever, but it shouldn't really matter. If you only allow HID devices, the mouse still works without getting access to the data on the stick.
Yes, but that isn't necessarily a good enough safeguard. See bigiain's comment about the USB Rubber Ducky... It would take more than a simple USB stick, but a device like that could disguise itself as a keyboard or mouse. Even if you blocked new disk volumes or something, a device emulating a keyboard could send keyboard signals to, say, open a terminal and copy files to/from a remote location.
You could use a keyboard as a data-storage device. Simply cat stdin into a file. That file would be a two-way communication program using the Caps Lock and other status lights for the reverse link. At that point it's as good as a drive, but slower.
