Not true. If the hydrogen is generated with renewable energies, driving a car such as the B-Class (Mercedes-Benz W245) shown in this video is in fact emission-free. A solar-powered hydrogen station was opened this week in Freiburg, relatively near to Mercedes-Benz's headquarters in Stuttgart:

http://www.ise.fraunhofer.de/de/presse-und-medien/presseinfo... (in German -- sorry, no English translation available yet)

Honda R&D Americas has such a gas station in Torrence CA since 2001. I don't know if it's open to the public though. The one in Freiburg is public.