We have a 2011 35i and we both love it. My wife drives most local trips while I do most of the long distance driving. We're both pretty easy on the gas pedal and average 24-25 mpg (at 6000-7000 ft elevation) overall.
I love the smooth effortless power provided by the N55 engine and, as an engineer, I appreciate its efficiency and refinement. Probably the best engine BMW builds. I'm surprised by all of the 28i sales when such a fabulous engine is available.
Dave @7500 feet on the plains in Colorado
2011 X3 35i - Blue Water Metallic