A lot of Story Games use transparent secrets. (The character might have secrets, but the secrets are open and transparent to the players.)
That is great and kick-ass, but I'm a player that also had great experiences of opaque secrets. (The characters might have secrets and if they secrets they are kept hidden from the other players.)
I also, like most people have really bad experiences of opaque use of secrets, because it really hard to do in a productive way, especially in tabletop games, because keeping them usually means spending a lot of time sending notes to the storyteller, or leaving the room to speak with the storyteller alone any other techniques that leads to less time spent on actual play for everyone. My personal horror example was a Vampire campaign where we spent 4 ours of our 5 hour gaming meeting sitting playing board outside the gaming room while someone else was doing secret stuff each meeting.
But I do like opaque use of secrets, when it done right.
I love it when something is revealed, and lot of little clues the other player left like breadcrumbs throughout the story, and all sort of small actions suddenly makes sense and the secrets reveal becomes an awesome plot twist both in and out of character. Or playing a game while knowing that someone else character might be a traitor, and trying to puzzle out who it might be, while immersing into the feeling of paranoia.
Because to me opaque secrets are a different experience from transparent secrets. Both are great, but different. Transparent secrets is like viewing the game as an omnipresent narrator, and not knowing them gives me the experience of viewing the story as first or third person limited.
So. I'm asking you all do you any great idea on techniques to play with opaque secrets in an awesome and productive way?