Historically, whatever tech is in the public view, there's usually much more advanced stuff that's classified. Considering the U.S. government has been pounding the anti-terrorism drums for a dozen years now, it's not beyond reason to think they've developed some incredible stuff we have no clue about.
Years ago, they already had a lot of this capability. There's also Duqu/Stuxnet, which the public only found out about after it was active for a few years. So I'm sure they've found enough storage space, perhaps even using companies like Facebook & Google to help them keep it. The real question is, what's their reaction time? How quickly is the gov't capable of responding to what's being said digitally. There's a ton of data every day, but it doesn't matter if you can cache it all if it'd still take you a couple days to detect what you need/want to find in it and react to it.