NSL definition from Wikipedia (yes syncretic Wikipedia)
Notice the definition of non-content information. That's a relief. It's the content that can be really damning. From 2003 to 2006 the Federal Bureau of Investigation issued 192,499 national security letter requests.A national security letter (NSL) is a demand letter, which differs from a subpoena. It can be used by US government agencies, mainly the FBI, when investigating matters related to national security. It is issued to a particular entity or organization to turn over various record and data pertaining to individuals. NSLs can only request non-content information, such as transactional records, phone numbers dialed or email addresses mailed to and from. They also contain a gag order, preventing the recipient of the letter from disclosing that the letter was ever issued.
Google's openness seems to contradict the notion that the recipient of the letter can never disclose the existence of the letter. That phrase in the definition from Wikipedia reminded me of the near future presented in the book: Super Sad True Love Story (Gary Shteyngart). The USA is run by a dictatorship known as The Bipartisan Party. Most chilling are the checkpoints and other security measures erected everywhere by a state obsessed with protection from terrorism, which of course becomes its own form of terrorism, right down to the bulletins warning citizens of the danger du jour and ending with the boilerplate statement “By reading this message you are denying its existence and implying consent.”