Started using my Mii (75) for longer journeys - a 32 mile each way trip to work, dropping off kids at school on the way, the A-roads, followed by motorway followed by some urban driving.
Just doing the school drop off and back (about a 5 mile round trip), my wife was getting low 40s mpg - measured accurately. Doing the longer journey, I get an indicated 57-58mpg on the way to work and 64-65mpg on the way home. Not sure why it is more economical on the way home. Hard to know what the actual mpg is on the longer trips as it still does some short ones as well.
But if I'm averaging about 55-60mpg in reality then I'm pretty happy. Compared with the big family cruiser I usually use, this probably halves my commuting costs once all factors are taken into account (maintenance, depreciation, etc).