Last night I got to attend a talk given by Robin Chase, Founder and Former CEO of Zipcar. Her talk was titled "Sustainable Transportation and Accessibility Research & Transformation", where she discussed how to decrease the impact of transportation on the environment and also using new transportation paradigms (such as shared car ownership) as a vehicle for bringing out mesh networks.
Mesh networks are simple: everything is a sensor and can connect to other sensors. She referred to it as "Ad Hoc Wireless networking", but I think that confuses the issue, because then people start thinking it just means WiFi everywhere.
What it really means is that all of these sensors and network devices can talk to one another, gather, share, and use information. For example, if every car was a member of the mesh network, they would all share traffic information, road conditions, and driver destination, perhaps. Then your in-dash display would update real-time traffic ahead of you as each of these cars shared their data. Also, you may be able to get internet down the line as you all shared a common network system.
Of course, now that you have all this data, how do you share it? Robin says she envisions all of this being built on open-source technologies, to allow for "innovation" (aka 'good hacking'). Open standards like GeoRSS could also be used to begin disseminating all of this data as it streams in and share it between devices. See the notes on Mikel's XTech talk for more inspiration along those lines.
If the devices are cheap (< $100), open-design, and run on open-software, this is a great future. If, however, it is run by proprietary, expensive technology, and closed standards, then you'll have a future where you get fast connections in your Ford car from other Ford cars, but no connection to all those BMW's or Toyotas on the road.