I think the answer is "you do the best you can".
OOC knowledge is always a problem, no matter how hard you work. The very fact of you knowing something changes how your character can react.
I'll give you an example.
(IC) Steve McSample: A supply of Vitoc, stolen, you say? How very unusual.
(IC) Mandy McMyCharacter: Hey! That sounds like you know something about it...
Nothing wrong there. It's a jump to conclusions, but there's enough in Steve's statement to make it reasonable.
Now add the following:
(OOC) Steve McSample: Heh. Steve stole a whole load of Vitoc recently.
(IC) Steve McSample: A supply of Vitoc, stolen, you say? How very unusual.
(IC) Mandy McMyCharacter: Hey! That sounds like ... uh. Oh. Nothing.
The fact that I know OOC prevents my character from guessing something that she might actually have guessed otherwise. Darn.
It would therefore appear that means that you should never talk OOC about your character. And indeed, if you want something to remain an IC secret, it's probably best not to share it with Channel OOC.
I'm not convinced, though. I think in many cases that the enjoyment gained from chatting about my character characters OOCly is worth the small risk of an IC "secret" getting out, and the small negative impact on other people's ability to guess. But it's not a one-size-fits-all-situations answer.