Jesse's Cafe has a great quote from Senator Frank Church, who managed to put limits on the NSA back in the 1970's that lasted until the post 9/11 era (he also chaired the Senate hearings into the oil industry that were the basis of "The Control Of Oil") - Frank Church: The Abyss From Which There Is No Return.
[America’s intelligence gathering] capability at any time could be turned around on the American people and no American would have any privacy left. Such is the capability to monitor everything: telephone conversations, telegrams, it doesn’t matter. There would be no place to hide.
If this government ever became a tyrant, if a dictator ever took charge in this country, the technological capacity that the intelligence community has given the government could enable it to impose total tyranny, and there would be no way to fight back because the most careful effort to combine together in resistance to the government, no matter how privately it was done, is within the reach of the government to know. Such is the capability of this technology.
I don’t want to see this country ever go across the bridge. I know the capacity that is there to make tyranny total in America, and we must see to it that [the NSA] and all agencies that possess this technology operate within the law and under proper supervision so that we never cross over that abyss. That is the abyss from which there is no return.