Around here a lot of places don't allow USB drives, but .. I think that's mostly a "Do Not Steal Our Data" policy.
Not, my real question is: Does that make sense? People talk about USB HID things, but .. I would expect that most keyboards and mice these days are using USB. So if you find a way to block USB drives for mass storage aka "Do Not Steal Data" uses, are you still open for all the "I type in exploits because I'm not really a USB drive, I can be a keyboard too" things?