Or, at least, this is what they’re willing to admit to for the present:
For the six months ending December 31, 2012, the total number of
user-data requests Facebook received from any and all government
entities in the U.S. (including local, state, and federal, and including
criminal and national security-related requests) – was between 9,000
and 10,000. These requests run the gamut – from things like a local
sheriff trying to find a missing child, to a federal marshal tracking a
fugitive, to a police department investigating an assault, to a national
security official investigating a terrorist threat. The total number of
Facebook user accounts for which data was requested pursuant to the
entirety of those 9-10 thousand requests was between 18,000 and 19,000
accounts.
And, of course, the fact that they’re handing over about 40,000 accounts per year doesn’t eliminate the NSA’s widely rumored backdoor access.