in my courtesy 320D, i managed to get an average of 28mpg over 3500 miles, including a fair amount of long haul motorway with cruise @ 85.......
I've done far less motorway work with the 330i and a lot more backroad blasting and i'm yet to have a tank average less than 22mpg in the same number of miles, and havn't done any long haul motorway trips (bar the 28 mpg 300 mile trip coming from collecting the car and even that was interupted by 60 miles or so of welsh B roads), and generally i drive quicker in the 330 as well.
so, 6mpg difference between a 2007 7k mile old 320D and a 2002 113k mile old 330i and the 330i has had a harder life.................makes me REALLY wish i'd bought a diesel