I just ran across a very interesting location based mash-up. Check out Cabspotting.org. They have gotten access to the GPS data from Yellow Cab in San Fransisco and created some really cool visualizations of the data, both in real-time and time-lapse. It is unfortunate that data like the Yellow-Cab location feed is not publicly available through a geoRSS feed. If it was, we would see much more of these interesting applications.