I use the 70-300mm on an E500 and I have been impressed with its performance. I have been enjoying reasonable success at airshows and motor-racing in catching fast action with continuous autofocus and often panning. At the Airbourne airshow in August, I was very pleased with the ability of the camera/lens combination to keep up with the Red Arrows (see below). Personally, I think this is a fantastic lens for the money.

This was taken with the 70-300mm fully extended at 1/1600th second at f6.3, ISO 200 and CAF.

Taken with 70-300mm extended to 300mm. Shutter speed 1/640th, f6.3, ISO 200 and CAF.