According to this Associated Press story, the tinfoil beanie hat crowd was right all along: "In an anonymous industrial park in Virginia, in an unassuming brick building, the CIA is following tweets — up to 5 million a day.
At the agency's Open Source Center, a team known affectionately as the 'vengeful librarians' also pores over Facebook, newspapers, TV news channels, local radio stations, Internet chat rooms — anything overseas that anyone can access and contribute to openly."