It a keeper

I bought this lens to replace a very low cost Sigma 70-300 DL lens that was a bit soft past 200mm. I also found that many of my pictures had some motion blur, especially ones taken at dusk or dawn. The Canon with image stabilization would fix that. Well it definitely has.
The new lens is much sharper at all apertures, even at the edges. Now I get good pictures with no motion blur at 1/60 even at 300mm. The image stabilization work very, very well.
For a non pro lens it is quite well built. The motor is quite fast and completely silent. The gyros make a very small whirring sound, but it is not bothersome.

The only down side is that unlike most lenses with an ultrasonic motor, you can not manually focus it without first moving the "AF/M" switch to M. This can be a bit annoying when putting the lens away, as it may still be somewhat extended.

I really like this lens. Its a keeper.