The difference between collecting meta-data about communications and monitoring the contents of the communications is that meta-data has more to do with mapping relationships between people, rather than watching what they are saying. The documents leaked by Snowden and his interviews suggest that NSA is collecting communication meta-data from a wide array of sources. Looking on Twitter, it seems that many people interpret this to mean that their personal communications have been compromised. That is correct, but the meta-data about relationships is often more valuable than the communications themselves and this detail appears to often be overlooked.
“Under the telephony metadata collection program, telecommunications service providers, as required by court orders issued by the FISC, produce to the Government certain information about telephone calls, principally those made within the United States and between the United States and foreign countries. This information is limited to telephony metadata, which includes information about what telephone numbers were used to make and receive the calls, when the calls took place, and how long the calls lasted. Importantly, this information does not include any information about the content of those calls—the Government cannot, through this program, listen to or record any telephone conversations.
This telephony metadata is important to the Government because, by analyzing it, the Government can determine whether known or suspected terrorist operatives have been in contact with other persons who may be engaged in terrorist activities, including persons and activities within the United States. The program is carefully limited to this purpose: it is not lawful for anyone to query the bulk telephony metadata for any purpose other than counterterrorism, and Court-imposed rules strictly limit all such queries. The program includes internal oversight mechanisms to prevent misuse, as well as external reporting requirements to the FISC and Congress.”
The reason that relationship meta-data might be more valuable than the communication contents is that meta-data is fact, but communication content is frequently unreliable. If a person contacts another person repeatedly, this almost certainly means that there is a relationship between them. It is pretty simple to filter out “wrong number” types of contacts by using simple frequency analysis. Frequent communications between two individuals likely mean that there is a strong relationship between them. Infrequent communications mean that the relationship between them is either weak or non-existent. This type of information is usually factual – most people are unlikely to counterfeit this type of information efficiently, though this meta-data mining system is not completely fool-proof. By comparison, the contents of the messages many people send to each other are complete rubbish – look at http://textsfromlastnight.com/ for some examples. Collecting meta-data can be easily automated, but reading messages almost certanily requires human analysts. Human analysts are typically a lot more expensive than processing meta-data. Meta-data is more accurate and less expensive to process than communications themselves and both of these factors make meta-data frequently more valuable than communications themselves.
Collection of meta-data is different from inspecting the communications themselves. Meta-data is often more valuable than the communications.