The pilot of the Piper PA-23-180 departed the controlled field for a flight to a destination which was approximately thirty minutes north of the departure point. The flight, which had been delayed for weather, departed after dark. At the time of departure, the planned route was forecast to have occasional rain showers and variable ceilings. After departure, the pilot of the aircraft headed north toward his destination, and opened his VFR flight plan. The aircraft then began a slow right turn to an easterly heading, and contacted approach control for flight following. After being given a discrete transponder code, the pilot advised the controller that he would be proceeding north at whatever altitude would keep him out of the clouds. But, the aircraft continued to fly in an easterly to northeasterly direction, and impacted a mountain ridge approximately six minutes after the initial contact with approach control. Prior to impact the pilot did not indicate any problems with the aircraft, or with navigation.