Ever since Carnivore (http://en.wikipedia.org/wiki/Carnivore_(software)) was uncovered, it's been obvious that a lot is going on behind the scenes. When the massive wire-tapping operation at AT&T (http://en.wikipedia.org/wiki/Room_641A) was brought to light, the scale and pervasiveness of this became clear.
This was years ago.
It's been safe to assume that all telephone conversations, text messages, instant messages, VOIP calls, email traffic, and all unencrypted web traffic is or could be subject to inspection, capture, and archiving. If it's not encrypted, it can be captured. If it is encrypted, it might be possible to decrypt it, you'll probably never know.
Facebook has long been suspected of being partially owned and/or controlled by the CIA (http://www.globalresearch.ca/facebook-the-cia-conspiracy/126...), and who could blame the CIA for taking an interest in such a valuable dataset. It's not clear if this is true, but if you're truly surprised that it's the case, you're far more of an optimist than I am.
The only thing surprising about this is that it leaked out, not that it was happening in the first place.