A study by J.D. Power found that only eleven percent of buyers were "very willing" to pay more for a greener car. They also found that women and people with higher degrees of education were more willing to pay extra for cleaner emissions and reduced fuel consumption. Car makers, of course, are very aware of this phenomenon. That's why there is so much effort to find cost effective (read: cheaper) ways of reducing fuel consumption and emissions. Customers are willing to pay for extra functionality that they can see and use like navigation systems and entertainment systems. The stuff they don't see - like the carbon dioxide coming from the tailpipe - doesn't get people excited enough to spend money. That's why in the short run at least we'll probably see more mild hybrids and direct injection than other, more expensive, technologies.
[Source: J.D. Power]