First of all, let me start by telling what this lens ISN'T. It is not a lens for a general shooter (unless you have that kind of scratch laying around). This is a fully-blooded professional constant aperture zoom lens that is designed to take the abuse of a working photographer. It is big. It is heavy. Most of the lens is manufactured from metal components. Much like other Zeiss lenses, even the lens hood is metal, and has a velvety covering on the inside to prevent light reflection. The lens hood is just a small example of the amazing attention to detail the designers put into this lens.
Performance: The Sony SSM motor is silent, and VERY fast (I used it on an a900). Accuracy is top notch, but be aware you may need to focus calibrate this with your camera (if it supports it) due to manufacturing tolerances.
Build Quality: Again, it's mostly metal. The finish is PERFECT, absolutely flawless (Which I expect for this price). The lettering on the lens appears to be laser etched, not painted. The zoom action is well damped, but not difficult to use. You can tell from the feel of the zoom action that there are some very tight tolerances being used on this lens. I feel like I could drop this thing on the ground and it would shatter the concrete!
Image Quality: Ok, here's the biggie. On full-frame at f2.8, the corners are noticeably soft at all focal lengths (looking at 100% crops). But as I looked through my photos, I remember thinking "But who cares? LOOK at that!" You can read reviews until you're blue in the face, but no one is going to notice the difference in sharpness across the frame. What people notice are the things this Zeiss excels at - colors. Contrast. Bokeh. All three are beautifully rendered. Typical Zeiss colors - natural, but vibrant. I've yet to find a lens that can match the blues of a true Zeiss. Contrast - very good, even from f2.8.
I've heard bad things about the bokeh from other reviewers, and I can honestly say that as long as you use common sense, the bokeh is smooth and buttery. Use at 70mm and f2.8, nothing but cream. I have used it several times at 24mm and f2.8 (to fake the look of the 24mm f2.0), and the bokeh did not disappoint there. I don't know, maybe I'm not as picky as other reviewers, but there are no problems here.
All in all, the Zeiss is a chunk of a lens that is every bit as good as the Canon and Nikon versions, if not better (not in corner sharpness, but in the things that really matter). It will last a lifetime of use. The only problem is the price. But if you're reading this review, chances are you are already familiar with the Zeiss name and know what to expect. The difference with this 24-70 f2.8 is that it is worth every penny of it's outrageous price!