A couple weeks ago, the CAFE Foundation, organizers of the Personal Air Vehicle/General Aviation Technology Centennial Challenges, held the The 2008 CAFE Foundation Electric Aircraft Symposium. From the announcement:
The event was well-attended by members of the science and technology media. Updates on the Aviation's Green Prize will be posted soon on the CAFE website. In all, the 2008 EAS made the dream of a 100 MPG PAV look a lot closer than most thought.
Here's a presentation from the Symposium by Brain Seeley on the Green Prize, part of the General Aviation Challenge. They're looking for 100 MPGe for the winner - seems like a popular milestone. That would be quite an efficient transportation mode, especially since planes don't have to go around obstacles like mountains, water, or other roadless terrain.
KITPLANES Magazine has more on the symposium and the General Aviation Technology Challenge.
The Green Prize isn't the only, or even the biggest, part of the GAT Challenge. There are also challenges for low noise, safety, and speed in the context of fuel efficiency, and several smaller "showcase" prizes for things like "best angle of climb". See the rules for more.