I worked pretty late last night, and rode home in the dark. I thought I'd be fine through the Presidio, and I was, but it was DARK. Being in the middle of the woods, knowing there's a wild coyote on the loose didn't put my mind at ease. However, concentrating on keeping my speed and cadence up as I floated to the top helped in that respect. The rest of my commute was pleasant. Without cars or noise it somewhat felt safer to be out on the road.
I love to ride in the dark. I used to go mountain biking at night with a full Night Cat light setup. I've even done a 24 hour race, where most of the fun was in the wee hours of the night. Your sense of speed diminishes as objects fly faster towards you, making you hyper aware of handling.