So, you are eager to own your first Zeiss lens with the Nikon D90? And wonder how it will be like. Let's call this a preliminary, prior to me actually getting it and shooting with it. But first, there are a few huddles we need to cross.
Huddle #1 - Manual Focus
Living in the age of autofocus, Nikon D90 owners are only forced to manual focus under video mode or specific image shooting moments where hunting is inevitable (e.g. shooting through a fence), and my experience tells me its not exactly a walk in the park. A lot of practice is recommended when you get that Zeiss glass.
Huddle #2 - Image Quality Review
Well, I am not too worried about this if I am doing it right, that is! The shallow DOF of using a big aperture can ruin every shot you take in an amateurish hands. Again, tons of practice is advised.
Huddle #3 - Assume Command and Control
It won't be that hunky-dory point and shoot situation anymore, as you attempt to hunt down that subject you wish to take manually. Imagine attempting to perform the AF-S or AF-C mode with your hands! But on the bright side of things, you will also no longer be subjected to the camera decision to allow shutter release. It will fire at your command every shot!
Huddle #4 - Price
At slightly a higher premium for only some model of the Zeiss family (e.g. Zeiss 50mm F/1.4), this can ultimately affect your decision on actually using them at all! If you ask me, I am personally looking only at the 50mm Zeiss lens at this point in time (to replace my Nikon 50mm F/1.8D).