I've got the 1.2 and it's sharp, the DOF is just super thin and the contrast drops off enough to where it might *look* like it is not resolving very well. On celluloid it needs a contrasty film/development combo to look as sharp as the slower lenses.

The 1.8, 1.5 and 1.4 are definitely better value for your dollar, given that the 1.2 can go for $500 and up these days.