Everything on the forums is OOC knowledge, and should never be used by your characters IG. I recognize that no one is perfect and that there's a certain inevitable amount of slipping that will occur, but you should never intentionally use OOC knowledge gained on the forums IG.
As a rule of thumb, I try not to share anything important on the forum that might affect ongoing events, though I do enjoy discussing events after the fact to get other players' perspectives on things.
Its a good thing all my characters can read minds and see all letters foreign rulers write!!! mwahahaha!