I like the feeling of night riding, especially on friday and saturday nights when everyone is going out and walking around. Great people watching times in SF. As stated earlier in the thread, the financial district takes on a whole new character at night, like riding through a canyon. I especially like riding through the really crowded areas like north beach, 11th street club corridor, irving street, and the mission, as well as the totally desolate places like the fi-di, sunset, gg park, and soma/south beach. Sometimes when I can't sleep on friday or saturday nights I'll go for a bike ride at 2 or 3am, very surreal.

As far as lights, in the early evening when there are a bunch of cars and ish, I'll use a rear blinky and a very strong front light. If I go riding past 12am I usually just use the rear blinky as there aren't really any cars out that late and, quite frankly, I'd rather that some of the bums don't see me coming, gives them less of a chance to ambush me (it happens).

Night riding is fun
Riding, zipping in the dark
Empty urban streets