I've commuted many winters in several northern US cities, sometimes in snow. I draw the line at icy road conditions, and at 10 degrees F. Slush is okay (especially now with disk brakes) and cold dry snow is okay. Winter bike commuting has never appealed to me. If I'm going to set up a winter camp, it'll be a snow camp on skis or snowshoes. That's fun once in a while. I have a nice down bag rated at -20F for that.