I've gone about 400 miles since getting my D back and so far all is well. My average MPG is up to 35.1 from 32.7 (~ 10% improvement, I reset when I got it back) and it feels more responsive. The weather has been crap in south-eastern PA for the past week so traffic has been moving differently than normal and I haven't been able to get a real data set.
It's hard for me to be really upset over this issue to date. My service dealer has been really good about handling the car. I've had various 2013 BMWs (X3, X1, 328i) to play with while they were working on it. I feel pretty good about the steps taken and the responses I have received from them.
So far, everything has been covered under factory warranty which runs out in March however, so that opinion may change.
I offer any and all information I can give you to help get action from your service dealers.