This is the variable you have to define first, do you only want to know about regular posters or lurkers and infrequent posters?

If we are including lurkers, it wouldn't surprise me that it's closer to the 100% mark. I say that from my experience of being surprised of the number of lurkers! At least once a week, sometimes 10x a week, I get a message from a friend or acquaintance on text or facebook that starts "So I saw you were saying on flyertalk.....". Almost always it's someone who doesn't have an account or who has never posted (and to me surprise it's often shortly after posting).