The only Zeiss lenses i've been really impressed with were made for cameras that say Leica, Hasselblad, and Contax....
In portland we've got a rental house that's got a full lineup of Zeiss lenses. I shot the 85, 50, 35, and 25 ZF's against the Nikon versions on a D800E. Results:
85mm
ZF vs 1.4G > 1.4G blew the zeiss out of the water.
50mm
ZF vs 1.4G > Looked damn near IDENTICAL.
35mm
ZF vs 1.4G > like the 50, identical
25mm
ZF vs 24 1.4G > Not even a contest, the Zeiss looked like garbage.
Where the Zeiss lenses are significantly better than the Canikon's is mechanics. They're fun to use and aren't built out of plastic. But to anyone who has a smarter eye than wallet, the optics are nothing to write home about in 2012.