I've been doing a good job of breaking the car habit and biking just about everywhere. When the windchill dipped below zero, I took a break for a few days.
Today's windchill is -18. Decided to give it a try today and bike to yoga (2 miles RT). Except for a few minutes of frozen eyeballs, it was totally fine. Snowed on the way home, so I rode slowly. For the most part, I was not cold, and it was better than driving.
Incidentally, since I started biking to yoga, I go more frequently. The one time I drove, I ended up missing class because I couldn't find parking. So there! Biking is awesome!