Look at that headlight-less punk in the Skyline Fog (pretty obscured for like 5ft away)!
Personally, I have a red blinkie on the back, and use that when caught in the fog. I don't bring my headlight unless it's going to be rainy or dark. Cars approaching from my front should be on the other side of the road, or I have real problems either way. Cars approaching from behind hopefully see the red light. On descents, I go at the speed my eyes allow me. If I can't see a driveway/entrance, I proceed as if there's a UPS truck about to pull out and kill me (usually is).
So I guess my vote is to have a taillight, and ride safely. Also, blast your earbuds and leave your helmet at home, as helmets are wussy.