The IS is indeed clearly audible, but m. E. not bothersome, and certainly not when you are traveling outside. The two selectable IS modes perform its function. The AF works fast and accurately.
The manual focus ring is blocked when you turn on AF, the lock button locks the entire lens, so that nothing can be adjusted unintentionally.
The image quality is absolutely OK and you have to look carefully before order to make real differences to form an L-lens focal length similar to (tested with an acquaintance and the Canon EF 100-400mm L IS USM on a 7D). The differences are there, my charge would personally but not worth it.
In the main use anywhere from me focal length range of 90-250mm (144-400mm KB) I am entirely satisfied with the image quality. From 250-300mm you have to make concessions, but even here the results are still unsatisfactory.
Conclusion: With the EF 70-300 IS USM you get a very good, high well-made lens, which does not need with its image quality to hide. For those who have such a focal length in his sights: to try Just looking in stores and check the images at home! And then of course: Buy!
