You may recall that towards the end of last year, I believe it was November, we were all shocked to find out we could no longer use USB thumb dives on our Coast Guard workstations. If you want to take a trip down memory lane I invite you to try and find ALCOASTs 570/08 and 577/08 as they spell it out. But for a refresher-

As you all remember, last November, use of USB flash media and removable storage devices was suspended on all DoD networks at all classification levels by the order of the Commander, U.S. Strategic Command (USSTRATCOM). The ban includes USB thumb drives, memory sticks/cards and camera flash cards. Use of external hard drives is permitted when "proper procedures" (scans) are followed.

The quote above is from a great piece on the subject of the DoD wide flash drive ban found on the DON CIO Blog- for those of us who don't speak Navy it can also be called the Department of the Navy's Chief Information Officer Blog. And in said piece (A Security Update: Flash Drives) the subject of "why can't we use 'em?" is alive and well. And the answer is quite simple: because DoD says so. But do note that the USB/External hard drive option that is noted. :)