It isn't quite so dark anymore when I commute but in the deeper parts of winter it was. Besides that, I have certainly gone on lots of rides in the dark, both in the summer and winter. Keep yourself visible, wear a hi-visibility vest (these are awesome, really it changes drivers attitudes I think on a subconcious level, they are just a bit more careful) and lots of blinkies and it shouldn't be a problem.

Here, sometimes I have gone out in the dark for longer rides (not my commute) in the snow around the city. It's very beautiful when you are in a secluded, dark, quiet place with snow all around and stars above you.