At 14:05 CDT, a Piper PA-34-200T porpoised on the runway during an aborted takeoff at Hobby Airport, substantially damaging the airplane but leaving the pilot uninjured. One witness said the airplane was airborne when the pilot reduced power, causing the aircraft to begin porpoising from nose to mains down the runway, culminating with a prop strike. Another witness said, Approximately halfway down runway 17 I heard him pull power, at which time the aircraft began porpoising progressively worse. Prop strikes occurred as he maintained directional control down the runway.