I like this article by Brock Yates:
http://www.caranddriver.com/columns/...ock-yates.html
This quote sums it up:
Now let's jump ugly about the whole situation and talk a little reality. The guys at Edmunds.com, who run hard numbers about the car business as well as anyone, estimate that a Prius owner would have to drive at least 66,500 miles annually for five straight years, or gasoline would have to soar to 10 bucks a gallon, to equal the cost of operating a cheaper, conventional Corolla.
And THAT ladies and gentlemen, is that.