Snowden unveils NSA Satellite SAURON Program targeting Citizens

Well, I don't doubt that it's technologically feasible. So in that light, I don't see what would stop them. We know they have absolutely no ethical problems with doing it. They have virtually unlimited funds and resources. They can always hire technical geniuses who won't have the same ethical qualms as people like Snowden.

They have relative secrecy. Even if a few whistle blowers spill the beans with vague details on what they're doing they still have plenty of shadow to hide in. They have many reasonably plausible excuses (not the least of which is the ever present fear of terrorism and the growing paranoia about lone gunmen).

I can't think of any reason why they wouldn't at least aspire to "Total Information Awareness". Even if it isn't already a reality, smart people know it is a wet dream these types of people constantly have on their minds.