I know I included this in my reading list post last night, but I consider it important enough to hit again.
You cannot trust the Snowden documents. They are incomplete and out of context. Compare the original reaction to Yahoos participation in PRISM to the revelation in yesterday's Washington Post article.
The documents, roughly 1,500 pages worth, outline a secret and ultimately unsuccessful legal battle by Yahoo to resist the government’s demands. The company’s loss required Yahoo to become one of the first to begin providing information to PRISM, a program that gave the NSA extensive access to records of online communications by users of Yahoo and other U.S.-based technology firms.
The ruling by the Foreign Intelligence Surveillance Court of Review became a key moment in the development of PRISM, helping government officials to convince other Silicon Valley companies that unprecedented data demands had been tested in the courts and found constitutionally sound.
In the aftermath of the revelations, the companies have struggled to defend themselves against accusations that they were willing participants in government surveillance programs — an allegation that has been particularly damaging to the reputations of these companies overseas, including in lucrative markets in Europe.
Yahoo, which endured heavy criticism after The Washington Post and Britain’s Guardian newspaper used Snowden’s documents to reveal the existence of PRISM last year, was legally bound from revealing its efforts in attempting to resist government pressure.
Any bets that this information was in the slide deck that outlined PRISM and that's why only a portion was released. Greenwald, Poitras, et. al. aren't interested in the truth, they only care about damaging America, and are not to be trusted. I expect that as other "revelations" are examined there will be similar issues.
(BTW Microsoft joined before the Yahoo case, but I am not clear on the circumstances so not quite willing to condemn them yet.)