The Supreme Court thought it settled the issue in January, but the debate over warrantless GPS searches won't go away. Now, one U.S. senator is concerned that the Department of Justice hasn't fully scaled back its searches and may be subpoenaing ISPs for the GPS data it can no longer get directly.
http://www.readwriteweb.com/mobile/2012/05/are-the-feds-still-tracking-your-gps-one-senator-wants-to-know.php