Not sure if anyone has seen this yet but I found this on a X3 forum........ Basically for those with mild winter temperatures (like it is here in Vancouver 95% of the time from November to February when the average temperature during the day is about 8 degrees celcius), most winter tires are terrible at braking and handling in warmer temperatures and the only tire (the Pirelli) that performs decently in the milder temperatures rated very poor for ice conditions. I had Pirelli winter tires on my previous 2006 330i and can concur that in places with a mild winter that rarely gets below freezing and rarely snows, snow tires are just too much of a sacrifice in noise, comfort, and handling for 95% of our winter.
For those in warmer climates (like Vancouver) that rarely snow I suggest instead of a snow tire an aggressive all season tire or a set of snow tires mounted on an extra set of wheels that you can take on and off yourself since you will only really need the snow tires on for an average of 2 or 3 days a year. Winter tires kept on for the winter make sense for most of Canada but in Vancouver you will just be driving unnecessarily around with soft, gooey, noisy tires for 95% of the winter.
http://x3.xbimmers.com/forums/showthread.php?t=751470