Interesting point about focus. I'm learning this technique too, and at f1.8 or f1.4 the DOF is so shallow that you have to be extra aware of the focus point. I'm including two photos from a family portrait session. The single girl...her close eye is in focus, and the away one is starting to get blurry. In the other one, the center girl is in focus, the one on camera-right is not bad, the one on camera-left is blurry, as she's closer. Just things I need to be more aware of with that razor-thin DOF.
Side-note...the 50mm 1.4 and 85 1.8 all focused fine on my 5d2, with the tifffen 2-8 stop filter, on max.