I'm a bit late on this one, but here's a new local app from Google Labs: RideFinder. Using GPS, it promises users the ability to "find a taxi, limousine or shuttle using real time position of vehicles."
This is novel and perhaps ultimately useful in a mobile application. But it's interesting in that, like Yahoo! Maps' traffic info, it's bringing real-time, location-based information to the Web.
In the near term, it will most likely be used by those who find it — it's not in evidence outside of Google Labs — as a White Pages-like source for local transportation services (e.g., SuperShuttle).