The recent Supreme Court decision limiting GPS tracking without a search warrant is almost meaningless. With iPhones and Droids and other smart phones, the government does not need to slap a GPS device on your vehicle to figure out where you have been, where you are, where you're going and how long it took you to get there. All it takes is a subpeona to your cell phone service provider.
From the Scientific American:
Mobile phone service providers log the list of cell sites to which our cell phones connect throughout the day. Mobile apps, more than half a billion of which were downloaded in the U.S. during the last week of December alone, gather data on the usage patterns of our wireless devices. In addition, mobile apps often track device location to the accuracy of a specific residence or office building, undermining the oft-cited claim that the data gathered is not "personal." Much of this data is collected and then sold with our consent, in accordance with privacy policies that few of us read before accepting, to a complex ecosystem of mobile application providers and advertisers. License plate cameras record our automobile trips. When we walk into a store, restaurant, office building, or sit in a taxi, images of us are recorded and date-stamped.I still remember the first 1 GB (gigabyte) drive I ever bought; it cost $197 at the computer show. Storage for digital files is now so cheap that there is almost no end to the information that can be stored and it will only get cheaper as the technology advances.
In the past it would have been impractical to archive all of this information. Not anymore. Retail hard drive costs are over one million times cheaper today than in the mid-1980's, and currently stand at roughly 5 cents per gigabyte. About $50 worth of storage can hold the information identifying the location of each of one million people to 4.5-meter accuracy at five-minute intervals, 24 hours a day for a full year. Data from video surveillance cameras is more voluminous, but storage cost trends are making it easier to archive that information as well.In short, the government can track you and hang on to that information as long as it wants.