Good point about visibility. One of the reasons that I don't mind bad weather is that I'm very well lit. I ride with three PBSFs and a MagicShine taillight, plus a MS 900 headlight and a P7 flashlight up front, lots of reflective stuff on my bike and a reflective vest with lots of material on it.

If I were riding with garden-variety taillights and no reflective vest, I'd stay off the roads during rainstorms or fog.