It wasn't so long ago that GPS was a technology reserved for the military and the super rich. Quite quickly, it's become something that just about anyone can take advantage of, with huge earth-wide maps such as Google Earth and GPS units being available in every retail store. While still somewhat pricey on average, GPS is becoming more available. Soon, it seems, ordinary handheld phones will be able to track each other for short distances. A company called Loopt, Inc is working with Sprint Nextel to offer a GPS tracking service that lets you know when a friend is within a half mile to 25 miles away.
Now, usually I know when my friends are in proximity because I can see them with my own eyes. But the applications and novelty of this do sound quite intriguing. Contacts (that agree to be tracked by other friends) show up as dots on a map. The idea itself is called social mapping. Conspiracy theorists will be sure to chew this up, but it does sound very cool.