I've only had my 2.0d for 2 months but can’t believe the mileage I’m getting. Around town 41.5mpg and on longer journeys 48-52mpg. I recently went from Newcastle to Cambridge with a top-box and bike on the rear and got 49.5 going down (with bike & box) and 51.5 coming back (with box)
550mile round trip plus still enough left for a few weekends. My last car (118i) only did 38mpg on the same journey.
I use the cruise control whenever I can and set it to 75mph (70 on my sat-nav). Don’t know if that helps save some fuel but saves on speeding tickets
Edit: our X1 also has the brake regeneration where the alternator only engages when you back off the throttle or brake plus auto stop/start which I believe gives 3% improvement