I just came back from a camera store, where I tried the Canon 17-85 IS EFS on my XT. I tried the Full Time Manual focus by putting it into AF and after getting an AF focus, I turned the manual focus ring to either fine tune it or focus completely on a different object. For example, I AF focused on a person's face, and then using manual, focused on an object a few feet behind him. Great feature, in that I would not have to focus, hold the shutter half-way, and recompose.
Here's the question: I found that the focus ring continued to turn, in either direction, past the point where it was affecting the focus. If I wanted to, I could turn it forever, without a change in the maximum or minimum focus. Is this a feature of the lens, and/or all Canon Full Time Focus mechanisms? Or, was I trying out a defective lens?