The public interest line is definitely not a clear one (as we've both noted). The funny things is that I read somewhere (but haven't checked it out) that the law in the U.K. regarding publishing private materials actually is based upon the public interest standard. So it is almost like the U.K. codified the ethics, wrapping ethics and the law into one, at least on that issue. As far as how to decide what is in the public interest, It is probably like many things in the law, such as the “reasonable man” standard in negligence cases. It really comes down to a case by case basis, unfortunately, and what the fact-finder (judge/jury, as the case may be) decides it is.