"As part of the European Union's commitment to improving road safety, Low Rolling Resistance Tires (LRRT) are to become obligatory from 2012. The fuel saving potential of using such rubber is 3%, the lower level of fuel consumption resulting from the reduction in the resistance to motion when a tire rolls." Taken from tire safe.
Lets see what happens to grip levels with the new breed of ultra hard tires. It's great to know you'll be saving 3% of your fuel as you're sliding into a ditch...