I own one!
I bought my 2006 1.8mpi 159 tourismo when the car was 4 or 5 months old. I upgraded from a 1.8TS 156 and a 1.8 petrol audi.
For my two cents the 1.8mpi is a good balance between economy and power. She sounds nice and throaty when she's pushed and my boss prefers driving my car to his 1.9 Audi A4 diesel.
I've got 84K km on the clock and the engine is still smooth and completely trouble free. The only issues I've had have been told to use 10 40 oil by the alfa dealer parts guy in limerick rather than the fully synth 5 40 stuff on two occasions. As a result the oil changes have been way (way!) overdue, but engine shows no sign of premature wear etc., thank God.
My trip computer always hovers around the 7.9l per km (35mpg-ish) on long trips (non-motorway roads here in ireland) and 8.4 (33mpg) on mixture of driving. But i'm kinda sensible rather than a stig.
BUT as much as i continue to love the car, if i could do it again, i'd get the diesel. It wasn't an option for me in 06 due to the extra cost, buts there's some fantastic value in the uk now on diesel.