After takeoff the aircraft was observed by witnesses to be in an unusually high pitch attitude which some witnesses described as a stalled condition. The passengers stated that after takeoff the aircraft began to shake but that the engine noise did not change. The aircraft descended in the high pitch attitude until ground impact. Examination of the aircraft revealed no evidence to indicate precrash failure or malfunction of the aircraft structure, flight controls, or engine. Calculations indicated the aircraft was about 150 over maximum allowable gross weight at the time of the accident. The center of gravity was 2.8 inches forward of the forward limit for the weight conditions. The stabilator trim was found at the 9-degree tab-down or nose-up position. The aircraft flight manual calls for trim near neutral for takeoff. According to the pilot's logbook the pilot did not have the required three takeoffs and landings in the past 90 days required by regulations to act as pilot-in-command carrying passengers.