Since forever. If you post a Skype log of another player and said player contacts them about it, they remove the log. I don't think they act unless one party complains though.
Yeah, well technically it's not an official rule that we have written to disallow it, but it's been a 'common courtesy/decent human being/fellow player/mutual respect' type of unwritten rule that has existed since at least, long before I ever arrived here personally.
It's just one of those very basic things that an actual forum rule shouldn't ever have to be written about.
I dunno, I always felt that if a discussion was relevant to a topic, it could be posted no matter what unless taken out of context. (Save for the context thread or something).
While you are right about relevance - yes, it's fine. But putting it to show how bad the other person is - is not fine. If somebody would create thread about metagaming and putting evidence with Hone's characters as example - it would be considered forum trial. Skype chat was something more or less equally incriminating.