I had an e90 330i for three days last week -- also as a loaner. (The X's tranny decided to stay in 4th gear.) I enjoyed it. Nice car. Very quick, very agile, and you're right, doc, very quiet. Tight chasis with little or no body roll. The one thing on which I disagree with Kewl is the steering, which I thought was "OK." I don't think it gives the driver enough feedback; it felt too "plasticky."
Mine did not have Nav or iDrive, so I did not get to play with them. Oh, and those cupholders! WTF were they thinking?!?!
Overall a very nice car, though.
Juan