I've only had my X for 1 yr...but one of the 1st things I bought last year were a set of dedicated snow tires (235/60/18 Michelin X-Ice xi2)...and I don't know how the all-seasons would handle in snow (my assumptions/thoughts were ditto what RB said in the post above)...but the dedicated snow tires made driving in last year's winter weather totally UNEVENTFUL...which is what you want.
Dedicated winter tires not only help with traction for acceleration, but also help with turning and most importantly...stopping. The tires you have mounted are as important as the traction control technology your vehicle has...in fact, dedicated winter tires helps xDrive/ABS/DSC perform their best.
The very last storm last winter (March/2013) dumped approx 15" of snow...and the temps were going to go up around 50 °F within the next few days...so instead of shoveling & snow blowing like my neighbors...I backed down the drive and up the street (totally unplowed) with no issues at all...as they all stood there...probably waiting for me to get stuck.
The pic below is what I saw when I peeked out to see how much snow had fallen and why I awoke to the sound of snow blowers buzzing away.