Wired has a great story on MIT Media Lab reseachers Nathan Eagle, who has been working on a project that uses mobiles to track were you went, how long you slept and what calls you took or bumped.
Using Bluetooth enabled phones Eagle stored the actions of over 100 people amd then was able to predict what people are likely to do next. He got it right 85% time with professors. Not only diagle his PhD it also allowed users to search just what they did and how much they did not.
They article also speaks of a new start-up that allows social introductions based on what you did which might be fun when placed against the likes of Ryze and LinkedIn.