I haven't worked it out, but it looks like it's doing around about mid-twenties to the gallon compared to my old Elan which returned early thirties. This is on a fairly easy commute to work. I think you can get it as low as you like when thrashing it though...
my boxster s is doing around 24-25mpg around town and 32/33mpg on the motorway. if you nail it however it is a different matter entirely and you could quite possibly see 3.2mpg