Steve,

Take a look at this article about the Prius from the current (Jan 08) issue of PC Pro:

http://www.pcpro.co.uk/columns/134751/epilog.html

My concern with it is that if you want to make an energy efficient car, surely you remove satnav, aircon and all the little toys that drain power and add weight?

Volkswagon have gone somewhere down this route with the BlueMotion models and I'm interested in BMW's new 1 series (48mpg from a 1.8 petrol is one figure I heard - I'm not too sure about that though) stop/start engine.

We're not there yet but we're in for some interesting new designs over the next few years.