Watched this last night
http://www.bbc.co.uk/news/technology-29032399Well worth a look on catch up TV if you missed it
It covered stuff I knew already TOR and the Silk Road.
Other stuff I didn't know like how Google and Facebook want to use wireless networks in cities to track where people are (even if they don't connect to them) and I guess send adds showing them were shops etc are.
They also said that all the tracking data they can get from web usage my one day be used to refuse medical insurance as what you do might increase the risk of certain diseases.