As I sit to post up this it is 3 degrees Fahrenheit outside. That's -16 Centigrade for you Canadians, and by the way, the windchill is -27C. I am a commuter, but I have common sense too. Here is my rule for commuting by bike. Keep in mind it's my rule. You can do what you want.
When the ambient air temperature is above zero and there is little to no wind chill, I ride. If the ambient air temperature is below 10 degrees and there is a significant wind chill, then I'm driving.
Why? Because I'm stupid, but not that stupid. I own a car. I do not have to ride. If it's dangerous to ride, then I don't. I am looking at riding well into my elderly years and cutting that short by being the "tough guy" and riding when it's 3 degrees outside with a stiff 15-20 mph. head wind is not going to further that cause.
I suppose I could get outfitted with all that specialty cold weather gear that folks use in the Artic to cycle with but honestly, I would use it so little that it wouldn't make sense to me to have it. This doesn't happen a whole lot: I might miss a handfull of commutes a year because of it, so it's no big deal to me.
Besides, my body can use the break now and then. It's good to rest. I think Mr.24 may have stole this quote somewhere, but I attribute it to him: "Rest as hard as you train." Makes sense to me! (By the way, Mr. 24 got himself a new squadra for '07. Did ya see?)
Then again, my wife is a Registered Nurse, so she is quite familiar with the effects of wind chill on the human body. She also wants me around in good health for herself and to help raise our two kids. Women can be that way, if ya know what I mean, and it's probably a good thing for me.
I suppose that's the real reason I'm not going to ride to work today...........
........and I'm good with that!