Original paper: http://onlinelibrary.wiley.com/doi/10.1002/aenm.201100152/ab... (free access until 27 June 2011)

This looks like a major breakthrough. Love the nickname - "Cambridge crude". As with all flow batteries, power density is low. But you could possibly compensate for that in vehicles with ultracapacitors which could also recapture energy from braking.