One interesting tidbit from the AWS re:invent conference in November: According to Stephen Schmidt, Amazon does regular "drills" where they pretend that a warrant has been received for a user's data, and they need to identify and isolate and copy all of it.
This tells me two things: First, that Amazon gets these requests often enough to have a well-tested procedure for handling them; and second, that it's still very much a manual process -- and that government agencies can't just reach in and grab data on their own.
As an alternate explanation: we practice fire drills, but that doesn't mean building fires are routine. Drills are indicative of something you want to get right when the time comes, not frequency.
This tells me two things: First, that Amazon gets these requests often enough to have a well-tested procedure for handling them; and second, that it's still very much a manual process -- and that government agencies can't just reach in and grab data on their own.