I still think it’s more to do with bad program file processing/reduction, a large file with a gamma effect sky not being reduced in the processing and size reduction with even gradient where there should be an even gradient. I’ve noticed sky artefacts in some skies from my A100 and A700 not even using a polarizer but much less so with the KM5D so I was putting it down to the size of the file to begin with, i.e. the larger the file the more it has to be reduced and the more pronounced the artefacts…sometimes, and one method I used to minimize them was to increase the file size with the quality slider, the more it is boosted (while keeping the 1000 pixel limit) the more the artefacts diminish, it doesn’t get rid of them completely but it sure helps.
Ed I thought Gaussian blur would soften the whole image but I see there is a technique for using it for gradient smoothing in this discussion, http://slodive.com/photoshop/how-to-correct-banding-in-your-gradients-using-photoshop
it got a bit involved for my three working brain cells, this next tutorial I haven’t looked at yet but it might be promising too. http://vimeo.com/4569340