"Riding in the dark - What are your greatest hazards?"
Other than the obvious answer of all the two ton killing machines around me, I'd have to say pot holes. Here in Seattle the roads are horrible, the basic maintenance has been deferred for over 20 years while the funds where used for other things, so a pot hole can literally appear overnight. Add rain, and speeding down hills to the darkness and the pot holes are seriously dangerous. I'm not sure any lighting system would help (see speed above). And no, I'm not going to slow down, riding fast is one of the things I enjoy most about cycling. I accept the risk, but it'd be nice if we just had decent roads.