I recently traded a '10 335i xDrive for an '11 328i Touring (M-sport, 6MT), and needed a winter tire/wheel combo. I have the Dunlop Winter Sport 3Ds on a Saab 9-5 Aero wagon and have put 5k miles on them, the 3Ds are a fantastic compromise between dry handling and winter traction. I live in Seattle, where the temperatures at sea level don't really dictate the need for winter tires, but the surrounding mountainous terrain is usually snow-covered for most of the winter - having winter tires on my vehicles means I don't have to think about going to the mountains, it's also nice to have the security of having winter tires fitted in case the temps drop at home. On the Saab the 3Ds are brilliant, very good traction on cold and snow, better than my 335i xDrive with all-seasons - even on hills.
On the Saab I went down a size for the winter set (215/55/16), but for the e91 BMW I wanted to emulate my summer wheel/tire combo as much as possible as I love the feel of the RWD/sport suspension/manual combo. My M-sport has 225/40/18s F and 255/35/18s R, for the winter set I went with a square system of 18 O.Z. Ultraleggeras (ET35) and 225/40/18 WS 4Ds so I could rotate.
There is a bit less rear traction while cornering with the square 4Ds fitted as compared to the 255 width summer Bridgestone RE050 runflats, but the ride has improved and the car is still very well planted in high speed corners. These WS 4Ds are quieter than the Bridgestones (that have 9k on them), and I'm amazed at the steering feel and tracking ability of these winter tires. I know the size choice has something do to with that, but my reasoning was that I'd be on snow 4% of the time and needed a tire that was capable in the dry as well. I have not had a chance to see how these perform in the snow, it's supposed to snow in the passes this weekend so I'll endeavor to get up there to see how they do.
Overall, I'm very impressed by these tires in the dry, and they're a great combo for the O.Z's on a 328 w/ZSP.