There are some disadvantages to compressed air propulsion. Compressed air is somewhat less efficient than electricity for running a vehicle. There is a limited range, meaning you'll have to fill-er-up more often than with gasoline, BUT like electricity, a vehicle can be "recharged" overnight, using a home compressor. CAT engines do not produce heat, so an alternate system would be used to heat the vehicle interior. Although the car itself produces no greenhouse gases, the energy used to compress the air may.
Tata Motors of India picked up the project last year, and hopes to have production models for sale in Europe and India sometime in 2008. The MiniCAT is projected to sell for about $7,000, and an all-plastic "People's Car" model being developed for India may go as low as $2,500.