Bests & Worsts Reviews from Amazon

I have owned two copies of this new lens (Nov 05 and Jan 06 builds). Both consistently front-focused on my Canon calibrated 20D. I kept the Nov 05 lens (much sharper than the Jan 06 copy when manually focused) and sent it to Canon for "calibration." The Jan 06 lens went back to Amazon with a note indicating how it was defective. The calibrated lens now provides very sharp and contrasty images, even wide open at f4 for 24-85mm. Image quality fades somewhat as 105mm is approached but is still excellent if the aperture is stopped down to f5.6. I've conducted controlled tests and this lens is just as sharp at f4 as my Canon 50mm f1.4 when stopped down to f4 and at 70mm it matches the image quality of my excellent 70-200 f4L. The image-stabilization really works and allows sharp photos of stationary or slow moving subjects to be taken in the same light as an f1.4 lens. I'm happy with the final outcome but Canon's poor quality control makes getting a good lens a matter of luck and/or determination.