Quote - my impression is that pornography and art are catagorically different rather than reflecting qualities on a spectrum

i think the easiest way to categorise it is that while artistic nudes may contain nudity, and may even be arousing, their primary purpose is not to arouse the viewer.

pornography's sole purpose is to arouse the viewer. any artistic value is merely an afterthought.

although they can overlap, i suppose. some pornography has quite a bit of artistic value (whereas most is just hastily thrown together crap)... and some artistic nudes, taken out of context, can be viewed as pornography.
renderosity's TOS seems to filter out most porn-type art though, and thats good enough for me. not that i mind seeing it, just that its not very conducive to a work environment or this type of community.