It all depends on what you are riding with. I was riding when the first snow fall hit, and while it's true for cars that just a tiny bit of snow is slipper. For bikes however, if you are riding carefully and not turning too quickly you should be fine. We had a snowfall on Saturday and I was okay.

Although I had my first almost fall yesterday night on my way home. I had to ride around a barrier and of course there was ice next to it. As I went around it my front tire did okay but my back tire slipped to the side and I put my foot down and was bouncing it for balance. After I saved myself and I just though it was cool how far the back tire swung around.