I've switched over to my winter beater bike. It has a few features that make it preferable to my three-season touring bike for this weather (other than just being more expendable.) First, it has platform pedals, so I can wear appropriate footwear with yaktrax on over them. Second, it has straight handlebars so I can wear heavy mittens and still work the brakes and those silly twisty gear shifts so I can change gears with the mittens on. And third, it's got two-inch wide studded snow tires so I can keep on truckin' in this weather. Other things I find useful are my heavy leather jacket, which keeps the wind out but doesn't overheat me when I'm huffing and puffing; heavy wool pants that I close off at the cuff with cycling straps -- which keep the breeze out as well as keeping the pants out of my chain; a merino wool balaclava under my helmet; and a nice long scarf wrapped around my neck and face. I don't normally ride more than a few miles at a time in the winter, but that regime keeps me comfortable while I ride.