It's not enough, but it's sure a start: with post-PRISM
According to top Facebook attorney Ted Ullyot, for a six month period "ending December 31, 2012, the total number of user-data requests Facebook received from any and all government entities in the U.S....was between 9,000 and 10,000." The company can only release so-called "bucketed" numbers in a range, but those 9-to-10 thousand requests correspond to between "18,000 and 19,000 accounts." We don't know how many of these requests were executed by Facebook—a Wall Street Journal source says the company "complied at least partially with 79%" of them. This, as FB is quick to point out, is a minuscule fraction of the network's billion-plus user base—but it is only a six month range out of many, many years of global popularity. It's also worth noting that not all of these requests pertained to FISA or national security-related investigations—some of them could have been for "things like a local sheriff trying to find a missing child," says Ullyot. We don't know.
What we do know is that the company claims it's "continuing to push for even more transparency," and what we can hope is that this will (quickly) translate into a better understanding of how, and how much, we're being watched.
Update: Microsoft followed suit, reports the Journal:
Microsoft later Friday said it received 6,000 to 7,000 requests for data in the second half of the year, from all U.S. government and law-enforcement entities in the U.S.