Canon returned my 100m-400m lens this past Friday, which it repaired under its warranty, shipping it via standard overnight delivery–all at no cost to me. I sent the lens to them via ground on the Friday two weeks prior. It turned out that the image stabilization was not working properly. They repaired the unit, and checked and cleaned the rest of its inners. I’ve had a chance to use it and it now seems to be working fine. Bravo Canon!