On August 3, 2011, about 1111 eastern daylight time, a Piper PA-30, N8314Y, registered to a private owner, collided with the ground during initial takeoff climb from Albert Whitted Airport (SPG), St. Petersburg, Florida. Visual meteorological conditions prevailed and no flight plan was filed. The personal flight was operated under the provisions of 14 Code of Federal Regulations Part 91.The airplane received structural damage to the left wing and airframe. The certificated commercial pilot and three passenger reported minor injuries. One passenger received serious injuries. The flight originated from SPG, en-route to Key West International Airport (EYW) Key West, Florida at 1110. The pilot stated upon reaching 85 mph, he over-rotated the airplane and retracted the landing gear. He did not retract the flaps. The airspeed decreased to 69 mph, and the airplane entered an accelerated stall. The left wing dropped down, and he immediately lowered the nose and leveled the wings. He lost directional control of the airplane and it collided with the ground. He further stated there were no mechanical problems with the airplane before the accident. Review of the Federal Aviation Administration (FAA) approved Flight Manual for the Piper PA-30 revealed in Section I, Limitations, that the stalling speed with the landing gear and flaps up is 76 mph. With the landing gear and flaps down the stalling speed is 69 mph. Visual examination of the airframe, flight controls, engine assembly and accessories by an FAA inspector revealed no anomalies with the airplane.