Just watched "World's Fastest Indian" last night on video. What an awesome job of aerodynamic streamlining that Burt Munro did!! How else could you get a 1920 Indian Scout motorcycle to do 201.85 mph! Ok, he had lots of homemeade engine mods also! You should check out the movie if you haven't seen it. With that kind of streamlining I would imagine you could get great mpg on a bike.
"If the engine ain't running it ain't using gas!"