If you have a cellular phone with you, the federal government can probably pinpoint your location to within 150 feet. The U.S. Court of  Appeals for the Third  Circuit recently heard a case addressing the level of privacy the public can expect in their cellular-phone use, in particular, information regarding when and where cellular phone calls are made and received.

The hearing was an appeal from a 2008 ruling by a Pittsburgh magistrate judge who denied a request by federal law enforcement agents for the cell-phone records showing the time when and location from which calls were made by a person under investigation. (In that case,  Philadelphia FBI agent William Shute testified that he obtained records 150 times in recent years to track the location of federal fugitives.) At the appellate hearing, both the Electronic  Frontier Foundation and the American Civil Liberties Union argues that the practice raises serious privacy issues, and Third Circuit Judge Dolores Sloviter seemed to  agree.

Sources:
http://www.philly.com/philly/news/local/84290122.html
http://www.foxnews.com/scitech/2010/02/12/fbi-knows-thanks-cell-phone/?test=latestnews
http://www.google.com/hostednews/ap/article/ALeqM5gjCPfFdmocBeGyr_-lqmLC_3CfcAD9DQS4Q84