Just read an article the other day on Yahoo about how they tested a Prius in Europe against a BMW 530d sport sedan (that's an inline 6 turbodiesel) with regenerative brake technology to generate power for a hybrid powertrain. It beat the Prius by 1mpg, despite being much heavier. Volkswagen is working on a diesel-hybrid, and I think there is some work going on along those lines and with other companies, where they are integrating the whole hybrid power generation and drive technology into the transmission to make more efficient use of wasted energy like deceleration. In the meantime, maybe a tried and true technology like a VW with the FSI (direct injection)system (my Passat gets up to 34 on the highway even with 4 people, and gets around 25-27 normal commuting.) There are some pretty decent small cars out there that are already getting high 30's or almost 40mpg without relying on questionable technology like hybrids (what happens when the battery pack goes crapola?)
