many good points in this thread.

you'll lose a few days due to streets covered in snow or ice, but most winters here are not _that_ cold. there will be a week or two of teens somewhere in there, but it's mostly in the mid 30s-mid 40s from november-march.

as said above, there's no bad weather, just bad gear.

your head, hands and feet are the hardest to keep warm. i highly recommend buying winter road cycling gear made from wicking synthetic fabric - the stuff is insulated and keeps you dry and warm.

the biggest mistake you can make is layering lots of cotton. you'll get sweaty fast, and sweat-soaked clothing will get cold. wicking layers take the moisture away from your skin adn keep you warm and dry.

for the feet, i'd recommend clipless because most warm winter shoes you'd want to wear will not fit into clips. you can ride durable road shoes with wool socks, then get heavy-weight waterproof booties to fit over them. not the most elegant solution in some cases (riding to the bar?), but an effective way to keep your feet warm.

remember that you'll be generating heat while you ride, so when you leave the house, you should feel cold.

also, if you're riding with a messenger bag, pick up cheap glove liners, arm and leg warmers, and extra hat in case conditions change or you're out late and it gets cold.

as for the bike, get good fenders and front and rear lights.