Possibly already been done to death, but I'm considering picking up the 50L.
I'm not one to dwell too much about design faults (if indeed they exist) and I appreciate there are multiple causes of the 'focusing issues' whatever they might be.
Reading around, the only two things I see myself needing to be concerned about are 'focus shift' and 'back focusing' - the latter is less important as it can be MFAd, but also reports of it are highly likely down to the extreme shallow DOF. The former is of more concern to me. When people speak about focus shift, I get the impression they're first acquiring focus on their chosen point, then changing aperture which I find an unusual approach. It seems unusual enough to me to think that that's what's causing the focus inaccuracy. Why wouldn't you just set aperture and acquire focus, then shoot.
I'm bothered about focus accuracy when taking shots like those below, taken with a 50/1.8 (is this also missing the floating element?) - can any existing users vouch for accuracy with subjects quite close? I understand if you shoot at 1.2, it's not going to shift because the aperture doesn't move when you release the shutter. It's only when you're stopped down a little.
I can't understand why there'd be a problem if you acquire AF *AFTER* you set aperture.