I have a 2010 X5 35d with 24,900 miles on it. Pretty consistently get 20 to 21mpg with call it 50/50 city/highway. We (wife and I) are pretty heavy footed on the car and highway speeds, when open are well up in the double digit range.

The only thing I hate is that damn lag when punching the throttle either from a standstill or pulling out of lane to make a quick pass.