While I wait for one of the informed regulars here to chip in, I just wanted to say I enjoyed mine a ton over the 4 days of snow-on-the-ground driving this year. Confidence building grip, helped no doubt by new winter treaded tires. I didn't get into a wide open parking lot for a slip 'n slide fest, but just normal street driving felt like I could tackle any cross street around here.
The older (non xdrive) couldn't split traction side to side, so I could see where some might grumble if encountering left/right issues.
I would like to hear some real world horror stories of the preface lift traction issues.
A decent write up on the newer xdrive system is here
Winter driving test: BMW xDrive - Autos.ca for a comparison.