Just got a Canon 70/300 Image Stabilizer lens....not an L-series. Now, I've shot hundreds of "speed" shots of race cars, using 1/60th shutter speed and panning to blur the background. No big deal. Tried it with the IS lens and the photos were surreal.....it looks like the IS is attempting to "solve" the background blur. Shooting at shutter speeds above about 1/160 cleared up the problem, but negated some of the sought-after blur. Shot the rest of the speed shots with the IS turned off. I'm just glad I wasn't shooting film, 'cause I got a lot of garbage before I saw what was happening. Question is, do the "L" series IS lenses do the same thing?