"The United States does not have any Internet Service Provider (ISP) data retention laws similar to the European Data Retention Directive. All attempts have failed:"
THEREFORE: Under what law was FB required to retain the data, which was eventually handed over under subpoena?
http://en.wikipedia.org/wiki/Double_Irish_arrangement
The location of its legal tax headquarters is up for debate; Additionally, Facebook has corporate offices all over the world in different countries: https://www.facebook.com/careers/locations Italy, India, Canada, New Zealand, Belgium, etc.
Clearly it's not just a "US" company and only has to follow "US" laws.
But I think i remember something about Facebook having european offices in Ireland, so for us Facebook users in the European Union it's the Irish and EU laws they have to abide.
But I havent got a clue about what law regulates theese things.