Current releases Traitor and Pineapple Express both feature main characters convinced that they are being tracked and monitored by the police or some government agency. In some cases it's true and in others it's just drug-induced paranoia, but the fear certainly isn't limited to fiction.
I have a friend that is certain that Fastrak, a company that created an electronic toll collection system for Bay Area bridges, is in cahoots with the police and monitors drivers' activity and whereabouts. It's a notion that seems laughable to me, but cell phone carriers are required to provide the ability to trace cell phone calls to a location within 100 meters or less.
For the most part e-tracking is reserved for emergency situations, but the FBI and the U.S. Department of Justice can locate a cellular customer and track their whereabouts. Is this something you consider or worry about?