What kind of uses could the Wavelength node be used for? One of the new features in 2.68 is the Wavelength node,
but I have yet to think of a good way to put this to use.. (though dispersion and diffraction immediately spring to mind)

What are some good use cases of this node? (And how is it different from a Color Ramp node?)
One might use it to get some form of iridescent effect (Wikipedia article). Elaborating on the idea that the perceived colour of parts of objects depends on the direction of the surface normal of each point on a surface with respect to our eyes. Compressing and rarefying a ribbed pattern around the scale of visible light wavelengths can change the colour we see as a result.