I had the chance to try the Hydrogen 7 yesterday at the SMMT test day, and a quick spin around the high-speed bowl at Millbrook showed that while the current 7 has been around for a few years now, it's still pretty good to drive, and also that its impressive performance and refinement do not seem to suffer when this specially-converted version is running on hydrogen.
In fact the Hydrogen 7 is capable of using either hydrogen or unleaded and can even be switched between the two fuels on the move at the press of a button, a change that is scarcely felt at all by driver or passengers.
I haven't looked into hydrogen in as much detail as I have bio-fuels, but I understand that BMW's approach of using liquid hydrogen to power a combustion engine is comparatively unusual; my guess is that this is thought by the company to be the best way of developing cars that can run on alternative fuels but still retain the sporty qualities drivers value in a BMW.
One drawback is that the separate hydrogen tank used by this model eats into the 7's boot space (see photos below), although this is probably no worse than the boots of Lexus' big hybrids, which suffer a similar problem. This does however, remind us of a big advantage enjoyed by cars that can run on bioethanol-based E85, where both unleaded and the alternative fuel can be mixed in any proportions in the same fuel tank and use the same pipework.
At the moment, only about 100 Hydrogen 7s are being built and there is just one UK fuelling point (at Wembley in North London). It's difficult to see big numbers of liquid hydrogen cars being sold, at least until the infrastructure is better developed, but at least BMW is pushing things along. In the meantime, though, the measures incorporated into standard models under the manufacturer's Efficient Dynamics programme, such as cutting, and then automatically restarting, cars' engines when stopped, and exploiting regenerative braking, are likely to have more of an impact.