When should I respect a person's request to keep information secret?

This is a good question. I think that many people act on implicit cultural norms on this point, which are based on ideas of self-sacrifice and altruism. The notion is that first, it is your "duty" as a friend to be burdened by disturbing or unsavory details of another's personal life. And then second, you are expected to sacrifice your own self-interest which might otherwise lead you to share this information with others for whom you think it relevant (as relates to your own selfish interest in the matter) and instead, keep it to yourself. I once had a roommate who had several girlfriends--he always eventually told them about the others, but one he had just started seeing didn't know about another we were going to visit, so he dropped on me that he had told her we were doing and going somewhere else for the weekend. I was supremely pissed off! I told him not to do that again, and it was very stressful for me, because how in the world am I supposed to try to remember a real reality and a fake one? I think this applies in general about secrets, happy or otherwise. Now does this mean a person shouldn't keep the information one knows about others private? No, of course not. I'm not going to share the facts I know of my friends' lives with others, just as I don't broadcast web feeds from inside my own home. Privacy is a legitimate value. But here, again, I think the principle of selfishness is a guide, and maybe a "selfish golden rule" -- for example if a close friend shares an intimate aside about some private sexual practice they like, I'm sure they do it with the implicit understanding that if I had shared that with them, I wouldn't appreciate seeing it requoted on fliers on all the cars in the my company parking lot the next day.