I was riding in the snow last weekend. Though slightly above freezing there was plenty of ice, snow, slush and a mixture of same with mud (whatever that's called) on a mountain bike ride above Big Bear Lake. It was pretty bad, plus I was getting colder by the minute.
Then it started to rain. I was expecting snow, but this was definitely rain. By the time I got back to our cabin I was very cold, very wet and very mud splattered (as was my bike). Still . . . a pretty ride in a cold and snow kind of way.
Thankfully there were sections of dry trail (see photo above). And, when I got home (Whittier) and went riding on Sunday it was a beautiful dry and sunny day.
http://www.strava.com/activities/98181194
So yes, I ride though the winter. Sometimes at altitude, sometimes at (prettty much) sea level.
Rick / OCRR