I use both a ZD and a Nikon D2x for landscape.
The main value of the ZD is IMHO:
1. Much better DR and smoother transititions to blown highlghts,
2. More pixels and sharper pixels (not by much though, but the D2x has very sharp pixels),
The advantages of the D2x are:
1. Much better battery life in cold weather (about 10 times better) - the ZD is VERY bad at that,
2. More DoF (everything else being equal),
3. Much faster interface (image display after shooting),
4. Better histogram,
5. Much more robust build,
6. More unfiform image quality with wide angle lenses (center to corner).
Regards,
Bernard