I feel the line is all in the intention. While the law may say differently, I do not believe nakedness alone makes for porno; it has to have a sexual theme. (Well, sexual above and beyond that implied by a naked person, anywho.)

This still makes for an awful lot of porno that's being passed for art in Japan, but as I have no problems with pornography itself, I've never bothered examining the issue.

Some of those weird fetishes freak me out, though. Damn sexually repressed Japanese people.