OK - I'm the "wussy" winter bike commuter since it doesn't get as cold here but I wear a polypro balaclava whenever the temps dip below 40. I'm asthmatic and as long as I can breathe warmed air I seem to do ok. I've noticed that the balaclava helps keep my cheeks from getting chapped to! I just have to remember to pull my glasses away from my face slightly when I stop so they don't fog up!

This mornings commute: 31 with a windchill of 20
Polypro Balaclava, Headband, Helmet
REI LongUnderwear, UnderArmour, LS Jersey, REI Cycling Jacket
Polypro glove liners, PE Lobster Claws
Fleece-lined leg warmers, shorts, overtights, REI rain pants
Smart Wool Socks, SealSkinz Socks, Neoprene Shoe Covers

Now I'll be the first to say I hate the cold and hate being cold and my commute is 6 miles downhill so I don't get much of a chance to really get warm before I get to work so I probably tend to wear more clothes than some of the rest of you.