I saw my response from last year; I want to add that my temperature threshold seems to be going down (I rode in 32-34 this week) and dark is no longer an issue. But the ice and snow, yes. My friend broke his hip last March, riding through a puddle on an AM commute, cornering, and skidding out, because the water he rode through was frozen (it had been down to 27 F that morning). I freaked out yesterday on my way home from any early AM ride, because some idiots on Barrett's Mill Rd. had their sprinklers on and the water had runout in the street. It was in the high thirties, but, still.
Again, I have the gear, clothing wise, but I don't have studded tires. I still would rather be x country skiing or snow shoeing when it's winter. If I get a job that is with a 7-8 mile commute when I graduate, I will consider commuting as much of the year as I can, but I am pretty sure snow and ice will still stop me.