You'll have to post some samples, along with the EXIF data (iso, shutter speed, aperture, focal length, etc)
Lenses with gigantic zoom ranges like that "tend to" not have the best image quality so that could be part of it, but it could also be technique related.
Yes, you will have to post some examples with the EXIF data, for us to have any idea of what the problem is.
My first though it that your shutter speeds probably aren't fast enough for that lens and my second thought is that that lens is not doing you any favors in terms of quality.
well, I would normally say it's probably user error. But with this camera, the single most biggest complaint is soft images. I returned my first body and the second was fine, however it still does not produce the same sharpeness as my 30D with the 100-400 @ 400mm.
Try to do another test using mirror lockup on a solid tripod and also use Live View at 10x.
what is your in camera sharpening set to? you have to decide if you sharpen in-camera on the fly, or if you sharpen on your computer when you downloaded them from the camera.
Bayer-pattern sensors do produce an image, which is not tack sharp. if you sharpen automatically in camera, you have no control ... you might lose information in fine structures if the sharpening is overdone. hence I would suggest to do all the sharpening outside your camera, adapted to the image you shot.
it is vry simple upload an image to a site loke photobucket and click on the little mountain and place it here. There is a more extensive tutorial here http://www.thephotoforum.com/forum/showthread.php?t=76568 . And I tned to agree, not having anyexperience with the 40D personally you might have a shutter speed issue especially with the lens you are using. My question is why would you put a lens like that on such a nice camera.