Those who wanted to talk about the NSA, especially critically on social media, may have refrained or at least paused to reflect on whether that was a sensible thing to do precisely because of the NSA dragnet. I personally initially paused and considered my action moreso than usual before I began retweeting and writing tweets of my own that are critical of the NSA's behavior and the laws that provide cover for its behavior.
Irrational or rational as fears of later repercussions for communicating opinions may be, when the subject matter is a principal organization that will ensure that very communication is never forgotten, I believe there is a chilling effect. It would be like hesitating to criticize Twitter on Twitter—you can imagine less savvy users would wonder, "Will this get me into some kind of trouble with Twitter?" Even now having long since put aside my worry about being critical of the NSA's behavior in public (yes, based on the tired axiom: "why would they care about me?"), I still suspect that I have squelched at least 10% of what I would have otherwise said.
Even as I write this now, it's impossible to not have a concern that in some (very unlikely) future, the NSA will put anyone who had been critical of their actions onto a "definitely will aid with all parallel construction requests" list. Irrational, sure. But difficult to put aside nonetheless.