I had the opportunity to hit some slush over the weekend in WinterPark Colorado with my E90 M3 as I came over the mountain (berthod pass). It did just fine, though I'll be getting dedicated winter tires soon. A little slipping around, but the traction control worked wonderfully. There wasn't enough slush to really judge it by since the tires sort of just pushed it out of the way.
Oddly enough, I was really impressed with the rain-sensing wipers.. Once on, I never had to touch it again and the driving went from a drizzling rain and traffic slop to blizzard conditions at speeds ranging from 15mph switchbacks to 90mph passing streaks..
btw, ran across a Saab Turbo-X test where they put it head to head against a Subaru WRX STi, M3, 335xi, and a Audi A4 3.2 Quattro on a dry and wet track. M3 won both dry and wet regardless of rwd versus the rest having awd. Driver was Jan Magnussen (25 Formula 1 starts, and triple Le Mans 24 hours wins for Corvette Racing) instead of some reporter or pr person.
http://jalopnik.com/380099/2008-saab...es-and-audi-a4