I got the Zeiss 21mm f/2.8 recently - amazing, sharp, beautiful color, "3D".
With my 5D mark III - Wow!
I want to go out and shoot just so I can play with that lens.
Keep in mind Zeiss is for Full Frame. Its way too much price for Crop if you are not using that awesome sharp edge. Though I may use my 21mm sometime as a "35" on my 7D when needed.
Yes it is manual focus but the camera's Focus Assist beep/flash confirms you are are on target. I actually love that - I can set my focus on what I want in the frame, then frame it up without AF messing it up. Yes, you can switch the AF point or switch to MF, but its just so pure with the Zeiss.
My lens strategy - Canon "L" on the long (got the 70-200 f/2.8 IS USM II for starters - want the 100 Macro and 400 DO). And Zeiss on the wide end (the 15 and 35 are next). And a mix in the middle (the new 24-70 II should be phenomenal, and the 85 is going to be a debate of sharp/microcontrast vs aperture/AF).
Keep in mind you can buy Zeiss in ZF or ZF.2 as a Nikon native F and convert to Canon EF-mount if you are thinking playing both sides of the line. As much as the D800 is interesting to me, I have confidence Canon will match or surpass the resolution in a year so I am sticking with Zeiss ZE and keeping it simple.