The NSA has gathered lots of data on the social connections of US citizens. 

According to documents provided by former NSA contractor Edward Snowden, the sophisticated graphs created from the information identifies American citizens' associates, locations at certain times, traveling companions and lots of other personal information. 
The NSA started allowing analysis of phone call and email logs to look at Americans' networks of associations for foreign intelligence investigations after officials lifted the restrictions on the practice in November of 2010. 
--Rob Archer