I don't think our enemies are going to gain any exploitable information from following my Twitter feed. Updates about how tired I am, my plans for the day, what I am having for dinner, or how much I love my wife will provide very little actionable intelligence. Al Qaeda isn't going to be able to do much with inane data like whether or not someone is stuck in traffic or how long the line is at the grocery store.
However, the value of the information provided on Twitter might be largely a function of who is providing it. If I send out a 'tweet' letting my Twitter followers know that I have published a new blog post- not much value from a national security or terrorism perspective. However, when the ranking member of the House Intelligence Committee sends out tweets like 'Just landed in Baghdad. I believe it may be the first time I've had bb [short for Blackberry] service in Iraq. 11th trip here.' and then proceeds to tweet about the movements of his party through the Green Zone, flying by helicopter, etc.- now that is actionable intelligence with some strategic value.
For the vast majority of Twitter users, the social networking service is little more than harmless and frivolous data. Apparently though, there may be good reason to restrict its use by certain individuals or groups to make sure they don't accidentally 'tweet' the activation codes to our nuclear arsenal or the truth about Area 51 at Roswell.

When a high ranking member of our Intel community uses Twitter inappropriately, it is a function of bad judgment as opposed to a function of technology.
Well, I don’t know about Tweeter but recently here in Mexico, the special police apprehended some hijackers who ask for for ransom.
When they interviewed them on how they get their victim’s information, they said it was through Facebook. They see all their victims profile, family pics, their friends , where they went to vacations, etc.
Since that news, I’ve seen many of my friends take down most of their images.
Oh my, and they get mad at us military wives for giving out dates over the phone while in the states!? What was he thinking? Makes me glad my hubby isn’t in Iraq… geez
Carlos, Don’t those people who were targeted know to set up their privacy rules? That’s a shame – and sad, too…
I agree with Chris in that it is not a function of technology (but how to use it wisely)