I can only tell you my experience and what I have read to date.
I drive an '06 325, sport with manual trans. It is my daily driver with a 160km a day being the norm. I have only minor problems to date with 106,000km on the clock.
Coming from an M Roadster we find it underpowered, although if you take it to the readline it's okay. There is NO torque at all. The benefit in all of this is that we are getting 850km or better from a tank. Don't expect any more from a 323 as the motor is working so hard there is no gain. I have read on E90 post that the 328 is about 10% worse on fuel. Most people are blamming the direct injection as it is really on the only difference as they are both 3.0L engines with single stage induction. The 330 has a triple stage induction which added 35hp give or take.
You will learn to hate runflats. I tried but gave up on them for a proper set of F1's. Snow tires are essential.
The E90 makes a great commuter car albeit expensive. I always feel safe, comfortable, and it is a real drivers car. The sports package rides stiff but it is worth it just for the seats. Beware that it is pretty low for a stock package and I am on my third front lip from winter ice damage. If your are interested in a good deal let me know, see the post below for details and a pic, just no CPO.