THEN Ubuntu.
Here's a theoretical tweet: "I have to leave at about 10PM to go on recon in Fadullah. Most of the guy in the platoon doing the patrol are okay, but Lt. Jones is incompetent."
You fail. That's 145 characters. Learn to tweet.
But in reality, I understand exactly what you're saying. There's more to it than that, though. Not only could a post on Facebook, Myspace, Twitter, et al compromise the soldier's personal, as well as our national security, but could you imagine the soldier that's talking with his girlfriend at home on Facebook on a military PC, while he's supposed to be watching surveillance footage on that same PC? The two seconds that he flips away from the window to answer his girlfriend COULD be when a terrorist jumped the dune and headed towards the base - who knows?
In addition, Myspace especially, is a breeding ground for all kinds of viruses and exploits. Surfing unprotected to Myspace on a personal PC is stupid, Surfing to Myspace on a military PC AT ALL should be grounds for a court-martial - knowingly and willingly exposing military equipment for sabotage.
"I go on working for the same reason a hen goes on laying eggs." - H. L. Mencken