I want this lens. Why? I want a really really really nice 50mm... since that's the focal length I'm "missing" (in terms of good glass). And I've got nice zooms covering the rest.
I've got the 1.8, but it's buzzy and noisy. Pretty nice images but autofocus isn't too reliable (possibly my camera aswell).
I want the 1.4, mostly for the build quality and better autofocus, but disappointed because it's only microUSM... therefore not as fast as my L zooms. Also, the copy I played with (my friend's) was unacceptably soft from f/1.4 to f/2.8. Might as well use f/2.8 zooms! (which he does, the 24-70 and 70-200 haha).
If the 1.2L is sharp sharp sharp from f/1.4 onwards, and decently sharp from 1.2L I'd be happy =) And ringUSM is supposedly faster, but there is a hunk more glass to move... so it might not be...