The Free Map of London is attempting to create, well, a free map of London, England by synthesizing freely uploaded GPS tracks of people walking the streets of London. This seems like a pretty good way to get updated data from what is becoming a large amount of data from the conglomeration of sensors people are beginning to carry on themselves.

Think about it, a person can very easily carry a transmitter, spatial locater, photographic and audio recorder, barometer, and chronograph as a matter of course. Now, link this information together and share it to a central databas and you have the potential to have a huge input of data for many possible uses.