Got my xDrive M135i mid November12, actually was the first delivered awd car.
What should I say, it's amazing, traction is superb and in combination with the new ZF 8speed AT simply stunning!!
We picked two M135s, my buddy got a sDrive. He now regretsnot getting the AWD! Especially in bad weatherconditions, needless to say it sticks like glue to the street.
Down side higher fuel consumption, additional 1,5l/100km! I really don't care about that though, safety first.
Regarding RFT, my summer tires are Michelin SuperSport something. The winter tires are Pirelli SottoZero RFT. Difference is massive, RFTs are muuuuuuuch harder. If possible avoid the RFT option for summer tires!!!!!!!