Much has been written on this and there is alot of often incorrect folklore. Upstream emissions are extremely important - Andy Revkin's post gets it correct - if you charge one of these cars with coal fired electricity it is no better than a conventional internal combustion engined car of similar size. If your power comes from hydropower or solar, it can be very green.
It is very important to get away from coal as quickly as possible. The economically viable alternative at the moment is natural gas, but it is not a medium or long range candidate. We need to be largely off of it in the next decade. I don't see that happening here or in many other places... but it is important to move as deeply in this direction as possible.