|I don't doubt for a minute that there is *some* sample variatiion. I also don't doubt for a minute that most of the "bad copy/good copy" talk you find on the 'net is utter crap. Quite a few of these people don't know at all whether the differences they are seeing are actually due to copy to copy differences, or their own technique. Some also have very unrealistic expectations of such a lens.
Wide open, this lens has such a narrow DoF that getting everything in focus across an image will be all but impossible. The lens definitely will not be razor sharp in the corners wide open, but that is not what we buy a fast 50mm lens for.
The 50/1.2 is a great tool for its intended use. That said, the cost premium for that half-stop of speed over the 50/1.4 is huge. The 50/1.4 is also a very good lens, but the build quality is not in the same league as to 1.2. Still, for a quarter the cost, it's an attractive option. I bought the 50/1.4 around 2004 and have hauled it around the world with me, and it is still going strong, so the build quality can't be that bad!