Why worry about NSA

From Stephen Walt:  (my emphasis)

Vigorous debate on key issues is essential to a healthy democracy, and it is essential that outsiders be able to scrutinize and challenge what public officials are up to. People who work for the federal, state, and local governments aren't privileged overlords to whom we owe obeisance; in a democracy, they are public servants who work for us. Right now, however, there are hundreds of thousands of public servants (including private contractors with fat government contracts) who are busy collecting information about every one of us. Citizens don't have similar resources to devote to watching what our elected and appointment officials are doing, so we must rely on journalists, academics, and other independent voices to ferret out wrongdoing, government malfeasance, corruption, or just plain honest mistakes. But if these independent voices are becoming more vulnerable to retribution than ever before -- and via completely legal means -- then more and more of those voices will be cowed into silence. And the inevitable result will be greater latitude for government officials, greater corruption, and a diminished capacity to identify and correct errors. 

In short, the real reason you should be worried about these revelations of government surveillance is not that you're likely to be tracked, prosecuted, or exposed. You should be worried because it is another step in the process of making our vibrant, contentious, and most of all free-minded citizenry into a nation of sheep.