The individual in question is a minor, the act damages the reputation of a legitimate news organization (a business, which by the way, lives and dies on public trust and the notion of truth), the ruse was aided by the US Attorney's Office.
It's not a PRISM leak by any stretch of the imagination but surly this registers a little above "meh" on your apathy-o-meter.
Law enforcement is well known to carry out undercover investigations during which law enforcement officers pretend to be someone else, or mislead people about their real intention. A classic example is offering a a suspect a drink out of apparent courtesy, with the real intention being to harvest the suspect's fingerprints/DNA from the drinking vessel. As long as the deception does not involve an inducement to illegal activity then I don't really have a problem with it. Deception as an investigative tool has long been considered acceptable by the courts as long as it does not 'shock the conscience' or involve a violation of the penal code. http://scholar.google.com/scholar_case?case=8766034093838378... (Frazier v. Cupp, 1969)
As an analogy, suppose you had a phone number for a criminal suspect. Would it be OK to call and say 'Hi, I work for the Seattle Times and I'd like to offer our newspaper free for two weeks, are you interested?' (this is a popular sales pitch with my local newspapers). If the person says yes and gives out an address and police start staking out that location (and delivering a copy of the newspaper every day), I don't think any court would have a problem with that.