Approximately 65 airplanes had flown to the airport for a fly-in. Excess airplanes that could not be parked on the ramp or in a nearby field were parked along the parallel taxiway, starting closest to the ramp. Terrain in the area the planes were parked sloped away from the taxiway, requiring airport personnel to park approximately 20 airplanes with their noses within three feet of the left edge of the taxiway. The planes were parked closer to the taxiway than they had during previous fly-ins due to recent rains softening the ground. The private pilot stated he was taxiing on the parallel taxiway to takeoff at idle power between 10 and 15 miles per hour and three feet right of centerline. He said he was cognizant of the wet ground off the taxiway and didn't want his wheels to go into the mud. The pilot cleared most of the parked airplanes when his left wingtip struck the propeller spinner of the third parked airplane from the end. The pilot then hit the last two parked airplanes before he was able to stop his airplane. The nose of the first parked airplane measured six inches from the taxiway edge, the taxiway was 30 feet wide, and the taxiing airplane had a wingspan of 35 feet. Airport personnel had issued a L-NOTAM for increased activity at the airport and airplanes parked near the taxiway. Interviews with the airport manager revealed the area between the taxiway and perimeter fence further southeast away from the ramp and accident location would allow airplanes to be pushed back approximately ten feet from the taxiway. Examination of the taxiing airplane revealed the leading edge of the left wing separated from the fuselage approximately six inches.