The pilot reported he conducted 6 previous uneventful flights utilizing both runway 18 and 36 for takeoff due variable winds. He elected to depart from runway 18 on the accident flight because the windsock indicated a primarily southwesterly wind. The pilot stated that the takeoff roll was normal; however, shortly after liftoff the airplane encountered a tailwind which resulted in a degradation of performance. The airplane began to sink and lose airspeed, and the pilot elected to abort the takeoff. The airplane touched back down onto the runway, and subsequently nosed-over, which resulted in substantial damage to the vertical stabilizer. The pilot, pilot-rated passenger and several witnesses reported a wind shift around the time of the accident. A weather report from a nearby airport revealed a 20 degree shift in wind direction and a 7 knot increase in winds with a 24 knot gust from the northwest during the hour that the accident took place. Postaccident inspection of the airplane revealed that there were no mechanical anomalies that would have precluded normal operation.