I ran some basic tests with the 18-200. Similar setup to what I did with the 50 (but I didn't fiddle with the AF fine tune). Didn't need to. Bottom line is the images are sharper than the images produced by the 50. So, other than its "see in the dark" abilities, the 50 is useless to me.
I just checked, and I've only got a few more days on my 30 day return window. Back it goes.
EDIT : Rassie, you and I cross posted.
I'm interested in understanding why you think this is a back-focus issue on the body. My "common sense" view of things is that if it were the body, then I'd see problems with my 18-200 as well. Since I don't, I'm blaming this one on the 50. But I'm also sure you know more about this stuff than I do, so anything you can do to take me to school would be much appreciated.