Sorry this doesn't answer you question but only poses another.. but have you really found yourself the need to manually focus? With the ability to spot focus on my Canon 5D, I've never found a need to focus manually and have found the auto focus capabilities of the camera to be highly accurate.
I've only been back in the game for a couple of months, but I'm finding myself quickly falling back into my 35 year old habits, which includes being anal retentive about controlling depth of field. I've done a bit of pseudo macro shooting with the 70-300 lens that has required going into the manual focus region which is identified as 'macro' on the lens. In low light, I'm also using manual focus a bit when the camera isn't all that great on its own.
Finally, I have no problem with the auto focus capability in normal and I don't really think it's giving any better or worse focusing capability than manual focus, but I guess since I'm only back in the game for a couple months, I still get off on grabbing the lens and controlling focus. I've always been a composition freak and I'm totally anal about controlling depth of field, including always paying attention to the entire composition of the photo not just the subject. So I rather enjoy having the ability to offset my blur a little forward or send it back a little bit, however the shot dictates. What it actually is all about is that I will typically experiment with my focus a little bit as I'm composing the shot...it helps me decide what is gonna be the best end result.
I guess I'm just saying that I enjoy the control that I have putting my hand on the lens, even though at this point its probably only 30 or 40 percent of the time that I'm manually focusing. It might be that, with time as I get more used to using the 40D, I'll shoot less and less without manual focus, but my habits do go back 35 or more years, so I rather doubt it.