I've seen this with two different lenses I own. Most of the time it's pretty easy to tell the actual focus point is on the AF selected, which is usually the middle AF point. But I have quite a few shots where it's really obvious the focus point is not near the AF point selected, but I only see this with the center AF point selected. What's bugging me is I never really saw this with my 20D, I'm only seeing it (occasionally) with the 40D.
For now, I'm chalking it up to needing to learn the new camera, hence the new focus points, in particular the new way the center point focuses. I've recently had major dental surgery and I am backed up with work issues so I haven't had the chance to get out of the house and take enough pictures to figure out why I'm having this issue. Just looking for feedback to help sort this out, because it was not an issue before. My 20D pictures may have been amateur shots, but they were focused where I expected them to be, or I could tell movement (mine or the subjects) caused the problem.
I think it's real obvious in the tractor photo the focus is not where ZB says it was. If I have many more issues like the ones I've posted I'll contact Canon. I wish I'd held onto the 20D as a spare for a while instead of selling it so quickly. That might've helped me troubleshoot this problem. Hindsight's a bugger!
Thanks for the feedback!