I do most of my grocery shopping in the middle of the night. I have a 24 hour grocery store nearby and I work weird hours, so I'll frequently be in there after midnight rolling my bike through the aisles and placing items in my panniers. Like others have said, good lights are important. I recommend Fenix and/or Dinotte for headlights/taillights; Planet Bike Superflash if you're looking for a cheaper (but much dimmer) taillight than the Dinotte. I also consider reflective clothing and bike mounted reflectors to be essential for riding at night. Boston Industrial is a good source for the reflective clothing. I like the Class III reflective windbreaker for riding on cool nights. The stripes on the sleeve really help people see when I am signaling a turn.

Once you get the proper lighting and reflective gear, riding at night can feel safer than riding during the day. There are less cars on the road, and the motorists that are out will be able to see you much better than during the day if you have a good lighting setup.