According to paperwork leaked by Mark Klein, they have/had a "Narus STA 6400" in the room. It's described as a supercomputer that sounds, to my ears, similar to Carnivore. I doubt that they even try to collect (too much data), and instead specifically look for things to grab from the firehose.
Or, according to TIA, compile giant banks of information on every user based on their traffic & purchasing habits. Combine this with your other online data & there's quite a bit on every person.
http://en.wikipedia.org/wiki/Narus
http://narus.com/index.php/solutions/intercept