i bought a 159 TI 2.4 Q-tronic 2 months ago. it's my 7th alfa(over a 10 year period, including a GTV cup and numerous 156 JTD's) and it's by far and away the best.
the gearbox is superb. a compete doddle to drive. smooth, and responsive. In terms of reliability, I read somewhere that it was a toyota box? maybe wrong.
in sport mode, the car rockets, and I love the fact you get engine braking. rare in an auto, and superb for spirited driving.
Economy wise, on good fuel(i know always run shell after problems running on supermarket specials) i get 39mpg(no really) driving at 70mph. and 34ish @ 80mph. My daily commute is 18 miles and is a 50/50 mix of B roads and motorway. I am happy with those figures. On supermarket fuel, it ran lumpy, started poorly, and struggled to return 30mpg.
The car has done 41k and is just 2 years old. It was a motorway mile muncher in its past life, hence the mucho cheapo price of 14k-thanks Daz @ Benfield(says a lot that I am happy to travel 160 miles to stick with his/their service, esp when Mango's is only 5 miles away)
Overall, I think the Q-tronic is underrated, rare, a bargain and very good.
'07 GT Blackline JTD, but a 159TI 2.4 on its way very shortly!