An update from me,
Sept 2009 Cooper D owned since July 2012 last year.
Driven around 12k miles since then (bought on 39k, now around 51k)
Now averaged 55.69 UK MPG on those miles.
Problems since I've had the car,
- Boot leak where seal was changed under warranty
- Very small bubbles in both rear quarter paint - both resprayed under warranty
- Rear bushes replaced under warranty from knocking suspension
- occasional not starting again after engine stop start has stopped.
- occasional hesitation around 1500rpm, not sure what that is
- just noticed lots of soot around turbo and on underside of bonnett (seen others with this problem)
It shall be going in again soon to hope fix the last 3 items on that list. Other than that its been a great little car.
Considering I went from an R53 JCW with around 25mpg... My running costs on fuel really were surprising
I shall update more on the MPG after more coverage, but still around 55mpg. That's actual, measured at the pumps and always inputted into iPhone app (Road Trip) and that calculates all my running costs. Highly recommended.