Ars technica in conjunction with NPR conducted an excellent experiment showing how much and what kind of information can be obtained through capture off the wire. This is the type of information that a national intelligence service would see by tapping into ISPs.
They simulated this by using a penetration testing device installed at NPR reporter Steve Henn’s house (with his cooperation).
The amount of information is amazing. Even seemingly inactive devices are constantly making requests and connecting to services.
While many connections to key services like email and banking are encrypted, most others are not, revealing a great deal about Steve’s research activities.
It is absolutely worth a read.