After 24.000 miles I am at roughly 38mpg in the 20dA. This is 70% Freeway (going 95-100 mph) and 30% city stop&go. If I have long stretches of 70mph on highways, it can go up to 43 mpg, but can also stay below 40 if the A/C is on and I have my 275 19" summer tires on. To be honest, I must say this is pretty impressive to me. I used to have one of the early X5 30d and was never ever above 17mpg, no matter how much I tried. Those two cars are exactly the same size, slightly different weight and the X5 had a six-stroke.
I am not sure while people still believe the 46mpg given by BMW are achievable in real life (other than driving through Canada off season w/o a single break).