I wasn't quite sure which poll response I liked best, so here:
I've been bike-commuting in earnest for a few years now, working up the gear and fortitude to do more and more of it year-round.
The bike is a 1980's MTB that has been converted to fixed-gear, and wears Nokian/Suomi studded tires in the winter. Pretty low-maintenance and grippy, although I lust for a fat bike at times...
For clothing, the Pearl Izumi AmFib tights are not cheap, but are nice and warm and durable. I wear wool socks and a long-sleeved merino wool base-layer, and Pearl Izumi "lobster claw" gloves when it's below 20°F/-7°C or so. That with a balaclava works for me down to about 10°F/-12°C. If it will be below that during the day, or raining, it's still tempting to take the car, though.
