I also have a 40d - I've already sent it in twice to canon service in CA. The first time they said they definitley found something wrong and fixed it... I couldn't tell the difference upon its return, using any of 5 different lenses (all canon lenses that ought to work fine with the 40d, including the 17-55 IS, which I believe was specifically designed for canon digital bodies).
I got it back... I too feel like a lot of times the images are too soft. I can't exactly figure out if it's overall though - as you can see from your own pix there, the closeup looked ok. I'm wondering if there isn't some kind of focus locking issue that somebody isn't seeing over at Canon. I have no idea how that could be possible, but I have been having pretty much the same problem. The lens type hasn't mattered. Nor apparently, has the focus mode. I generally just use the center focal point and single shot mode, and I still get results similar to what you are seeing.
I also own the original series Digital Rebel, and that camera even on +1 sharpening was plenty fine - on my 40d, I've got the in-camera sharpening cranked up to 7 now to make it look comparable.
The only other thing I can think of to do at this point is do a side by side comparison of both cameras with exact similar picture-taking circumstances, and then send the results to canon and see what they say.....
grr.