That's very poor economy, unless you are doing purely urban driving. COuple of people in my office with e90 320d's and one gets 45mpg (pre-efficent dynamics model) and he drives it really hard all the time. The other gets 49mpg from a newer efficent dynamics model.
I'm averaging 42mpg in a 330d, and I do like to squirt it on a fairly regular basis!!
2008 E92 330d M-Sport, Sapphire Black, 19" 225M's