Several at out work commute all year round, rain, snow, ice or sun up here (Ontario). The main thing is to dress for the weather, and by that I mean don't over dress - you'd be surprised how warm you get riding. Layer, and remove as necessary. Although temps don't usually go below ~0F in the winter, we have had rides down to -30F. I usually wear a long jersy, thin fleece (100 weight) and a shell all winter long. Everybody is different, and certain parts of the body get cold - for me it was my toes & fingers, so spending some money of good winter cyclling boots & glove (insulated Shimano DH boot & Pearl Isumi Lobster Claw gloves) was what did it for me.
My commute is ~10miles one way, over 1/2 is trail, the rest road. I usually use a SS in the winter instead of a fixie as I find the ability to coast is useful on the really slippery stuff, or going downhill in axle deep snow. Deraillures get ice covered and salt damaged. I'll ride the trails until I can't get throught the snow (which is ~ axle deep, depending on the type of snow), then I'll use the road few days untill the trails get packed enough to ride on. Disc brakes are very useful, if your roads are salt covered, I'd recommend hydralics. Either go with a good cheap Ti frame or a beater - steel and aluminium joints get fused by galvanic corrosion if you ride salted roads (I've had many unremovable parts - like Al seatpost in steel frame, or my current steel Time axle in my Raceface cranks
all were covered with antiseize prior to installation). Use half decent seal hubs (shimanos work great). A decent coil/oil fork is great on the frozen trails, but if you're mostly on road, a rigid fork is the way to go. And fenders.