Came across a review of the new ZF 18mm -- not too flattering, it seems. "Carl Zeiss Distagon T* 18mm f/3.5 ZF showed somewhat mixed results in the field. The lens excelled in the center throughout the aperture settings on both full frame as well as APS-C cameras. However, border image quality was a little bit mixed, with f/3.5 and f/4 delivering somewhat softer results, and visually, there was a noticeable change in quality when going from the wide open aperture to f/8 or f/11... you should probably still look into a few alternatives before plunging that much money for the newly released Distagon T* 18m."
http://slrlensreview.com/content/view/498/51/
Would be interesting to compare it to the Nikon 14-24 2.8. From what I know, the old Distagon 21mm gives better IQ corner to corner...