I have the 320d manual.
Had the car for 1 ½ years and average consumption is 50 US MPG (as you see below from my fuelly profile)
However, put on cruisecontrol on 50-60 mph and you can expect to see numbers as high as 60+ US MPG
. Lowest I've achieved is 69 US MPG to/from work one day with zero traffic and 90 % highway at 55 mph (Yes, my bord comp. is very accurate, always correct with manual calculations from fill ups) Not bad!
Also recently got the M-performance power kit that bumps power to 200 hp and 309 lb ft. I havn't really noticed any drop in MPGs, maybe a bit at higher speeds but nothing significant