Cars such as the Viper have curved windshields, but they are very pricey.
As far as for use in a car ( a complete enclosure ), there is the issue of rollover protection, since there is only the glass around you, and also the inside of the car becomes a huge oven in summertime.
Not to mention that there is no way to easily roll down a window on the side of the car.
Aerohead - i see you beat me to it !