Well, Phatbimmer, the only reason for me thinking that there is a difference in quality is that I've never seen a BMW (or Mercedes, Audi or another German brand) on diesel start with a real cloud of blue smoke on cold days (like mine does over here, and it has only 8000 miles on it) in Holland. That's something for real old diesels. On warmer days I have no 'problems' at all. Since diesel fuel is self-burning (it doesn't need ignition plugs) and is known for having problems with self-burning/igniting at cold temperatures I know they put in additives in the wintertime in my own country (so-called winterdiesel). But once the engine gets a little bit warm, no problems with U.S. fuel at all.
The specs are: Inline 6 cylinder, 24 valve turbo diesel (common rail with intercooling), 2.993 liters, 204 hp @ 4000 rpm, 410 nm from 1500 rpm on. That will give it a top speed of 242 km/h (330i has a top of 250) and from 0-62 mph goes in 7.2 seconds. But it's power lies in quick sprints in almost any gear while already cruising. I have an average of approx. 35 mpg.
The reason why a lot of people drive diesels in Europe (well, at least in Holland) is that fuel prices are REALLY high (around 5 dollar 20 for a gallon of Euro 95 gasoline) and diesel is a little bit cheaper (around 3 dollar 80). Reason for that is that all the big trucks drive on diesel and a higher diesel price will kill a lot of companies. They do tax you more on a diesel car, but since it does more mpg and I drive a lot it's a lot cheaper for me on diesel.