Probably this post doesn't belong here.. But anyway.
I tried out the 85 f1.2 (new one), the 135 f2 and a 100 f2.8 macro.. As far as bokeh is concerned all three performed pretty close really, with the advantage going to the Macro lens whenever I needed to get close to a subject, as the OOF areas were just as nice as in a similar shot with either of the two L lenses.. I was a 85 f1.2 "afacionado".. and was rather taken aback by the comparison.. My lowly macro lens which I hadn't really considered as a portrait lens was really excelling! I also compared the 70-200 f2.8 IS lens, but the bokeh wasn't nearly as good as any of the other lenses. I suspect that this has to do with the IS function, because the non-IS version I traded up from seemed quite a lot better.. So what does this have to do with the 50 f1.2? Well, nothing really.. just a comparison of similar lenses (i.e fixed-focal reasonably wide lenses).
One area where the f1.2 lens (again, the 85mm one, I haven't touched the 50mm yet) really shines is low / available light photography. Night shots appear taken in daylight, and the bokeh is quite buttery, so the 50 should be similarly good. When comparing night shots with the 85 and 50 f1.4 the light quality of the 85 was simply outstanding
Ultimately wanting to own these f1.2 lenses becomes a question of need as well as prestige. Unless you take 100% of your shots in no light, and cosnistently use the widest aperture, they are probably unnecessary... A wonderfully expensive tool for a very specialised photography no doubt, but one that most of us should at most covet, but never actually shell out the money for. It's like a porsche.. take it for a test drive if you can, rent it occasionally, but own it?