I would love a GPS "swarm" application that uploaded aggregate tracking data for everybody who ran that application on their N800. It could then use the aggregate data to show average traffic speeds everywhere the application was in use.

By extension, you'd know where the traffic spots were because you'd see the places where the "swarm" was stuck.

Of course, you'd need a decent install base for this to work, and you'd have to remain online the whole time.