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The Unsharp Mask function can be used to remove distant landscape haze. It also improves contrast overall, but has a tendency to blow out highlights when the radius is set too large.

In this example, I concentrated on cutting the haze and bringing out details of the sandy bay in the lower section of the image. Experimentation can yield different emphasis, however because of the difference in distant between near elements and far, it can be tricky to get the whole image haze reduced - it's always a compromise.

Before shot:


After:



USM settings used: 75% amount, 15 pixel radius, threshold 1.
I used 75% to exaggerate the effect so it can be clearly seen. You might like to use a little less for normal pics. 15 pixel radius - because the size of the image in the example is small, 15 was adequate. Usually, you'd be using quite a lot larger. Experiment to taste. Beware that too large a radius will smear highlight details to white (especially combined with a high sharpening value).
This can also be applied to other photo editing programs that uses a gaussian blur technique on a background luminosity layer to increase apparent edge contrast.

Nikon Capture 4.1xxx can do USM also!
And it depends on the lens (and probably other things).
Top of the line lenses with great sharpness will obviously require different USM settings than consumer grade lenses with so sharpness.

At least, this is what I found in my experience