Not all GPS/Location tracking is created equal. I have been arguing that there is a difference between discrete short-term tracking of an individual when a crime is suspected, and long-term surveillance of an individual. In the case of long-term tracking, the aggregation of tracking data can reveal medical, religious, and political information that otherwise would be considered private. You can read my views in an October 6, 2010 post and in an upcoming law review article. I also take on Yale on this issue here.
The government does not seek location tracking records for a single mobile phone over a continuous period of 21 days; instead, it seeks records for one telephone for a three-day period and a separate six-day period weeks later, and also the records of a different telephone (albeit one allegedly used by the same investigative subject) for a twelve-day period several months later. Even if it would be just as impractical for the government to conduct physical surveillance in lieu of electronic tracking for such shorter periods, I cannot assume that the information gleaned over such shorter periods, separated by breaks of weeks or months, would necessarily be as revealing as the sustained month-long monitoring at issue in [other cases].