This is a fascinating talk about how the Italian police identified a CIA operation in 2003. It points out just how much information your phone gives out, and how the government can use it to piece together way more than you think. It also points out just how hard it is for even intelligence professionals not to get busted (hint: really hard).
Note: this talk was given at the 2013 Black Hat Briefings (perhaps the world's most interesting security conference). I was there, but didn't attend this talk. I did live blog General Alexander's keynote address, though. My skepticism at the time was perhaps more percent that I'd like:
He talks a lot about internal NSA training and individual auditing. The big concern isn't rogue NSA employees, but a directed program from NSA management. He isn't addressing this at all.*cough*Russian dossier/FISA*cough*
Your cell phone is the Police State's best friend.