I agree with the above comments regarding portraiture, the down side being that the majority of Poser users use it for just that reason, making portraits.

Skin material conversion by Lux (or any 3rd party renderer) is faced with the issue that material conversion will always be qualitatively inferior to that of the original in that it is only mimicking the original material. An anology would be transcoding loss with video where conversion will always result in output inferior to the original. Whether or not the loss of quality is perceptable to the human eye in a render is another matter.