Network thinkers know that to effectively monitor a network, you don't seek out the edge nodes, you find the central hubs and monitor them — through them you will have access to most of what is flowing through the net. Below is a network map of the Autonomous Systems [AS] that form the backbone of the internet. It is easy to find the central hubs in this network. Load the 20,000+ nodes [each AS is represented by a node] and 48,000+ links [a data flow between two ASes is represented by a link] into a social network analysis software program and have it run the Betweenness or Connector metric. These two network metrics reveal how central any node is in keeping everything interconnected. The hubs will be reveled by the network metrics. In the diagram below the hubs are sized by their Connector score -- the higher the score, the larger the node, and the more network paths flow through this node. The colors are randomly assigned and have no meaning.
Most of the large Internet hubs are located in North America.
The largest hubs [AS] are mostly telecomm companies, internet infrastructure providers, and organizations of the US government. Most of the large Internet hubs are located in North America. You can get a pretty good picture of what is flowing through the whole internet by monitoring just a dozen or two of the largest hubs. An example of how these main hubs can be tapped, and utilized, is told in the story of Room 641a of SBC Communications in San Francisco.
Whether the NSA has a direct tap into your favorite social network, or search engine, we may never know. Maybe they don't need it to capture most of the information flowing on the Net? They just apply the Pareto Principle and get most of what they need.
How will the rest of the world view their dependence on the internet, with the U.S.A owning and monitoring the the key hubs daily?