I ride to work year round too, unless it's impossible, like the first day after the holiday snowfall in NYC in December, when I could hardly get out to the sidewalk. I see quite few dedicated commuters too. Although the numbers drop significantly when the temps get below freezing or when it's snowing. I'm never the only bicycle commuter even in the worst weather though.
I also run errands and do shopping on a bike in Winter too. I actually found it easier than stop-and-go driving in mad traffic.
Adam