The best thing about the Prius is that it achieves its high fuel economy without sacrificing size or performance and, most importantly for global warming, without being a diesel. There seems to be a lot of confusion on this point, so let me elaborate.
Bottom Line: If you care about global warming, don't buy a diesel car (certainly not in this country), and if you must buy a diesel, only get a new one with a very good particle trap. [Does this mean that Europe's massive switch to diesel was not good for the climate? In a word,"probably."]