I had a Kawasaki 360 but it only got 40 mpg....and with a 3 gallon tank that does not get you too far. I agree with Canie that you would expect better gas mileage from some of these cars. I saw something on the Smart Car, which is tiny, and it really does not get that good mileage. I think the problem is that it is chopped off in the back and has the same wind profile (cross sectional area) as a bigger car...and the lack of a back to that car may make it less streamlined. It is also probably more powerful than it needs to be.
We keep our cars until they die, and our older car, a Civic, is only 11 years old and we may get 5 more years (or more). By the time that dies there should be something good out there for mileage. Electric does not do the global warming trick here, as a lot of it is from coal.

We had an energy audit of our house yesterday...interesting: the guy did not like compact fluorescents. It may be a real bad idea to put mercury in a household thing like bulbs: these need to be specially disposed of and that is not likely to happen all the time.
Chris