I bought the swedish photo magazine "Proffs Foto", (which in english means Professional photography), and there are tests between AF Nikkor 50mm F1.4 and Zeiss ZF 50mm F1.4 and also between Nikkor AF 85mm F1.4 and Zeiss ZF 85mm F1.4. The tests included sharpness, bokeh, how the lenses handled bright light, colors, distortion and vignetting. The tests were performed on Nikon D2XS and D200 bodies.
For the 50mm lenses the sharpness, distortion and vignetting were equal. They stated that the bokeh was better with the Zeiss lens (there was hard to see any large differencies on their s&les). The Zeiss 50mm F1.4 has better colors (more realistic) and handled bright light better. I can verify the conclusions from the magazine since I own these lenses myself.
The Nikon AF 85mm F1.4 has a reputation of being a very good lens with good sharpness and good bokeh. The Zeiss lens handled bright light better and has better colors. Vignetting and distortion were non existent. The sharpness was equal at F1.4. At F5.6 the sharpness was better with the Zeiss lens in center and corners (the Nikon has very good sharpness at F5.6 but the Zeiss is better!!!). The bokeh was MUCH better with the Zeiss. The colors are more accurate with the Zeiss. They had shot portraits with both lenses and the only "parameter" that was different was the lens. The skin tones were much more realistic with the Zeiss lens.
I know that this are well known "facts" for most people on this forum but I got a bit exicted. I have never thought of the importance of color rendition of a lens. With other words I have never thought the difference was so significant. I found it very interesting that they tested colors, bokeh and ability to handle bright light. These features are often not taken into consideration in other lens tests. Also interesting to see the better sharpness of the Zeiss lens in the cropped sensor size, especially in the corners.