No one that I know who owns a Mini, including US, has been thrilled with the gas mileage! It is a GREAT car and is lots of things but fuel efficient is not one of them!
And FYI, if you haven't 'heard' someone say it yet, there are no actual fuel ratings available yet for the gas smart that we are getting here in the states...the "40-48 miles per gallon" is an estimate and when you go drive a smart they ARE SURE to tell you that they really have no idea what the actual MPG will be yet.