I don't know if it would be a good thing for a coach to post on a message board, but I have to say, it would be refreshing if it came out that one was lurking.
You always hear that the big money guys have their ear.
And while I wouldn't pretend the insight on message boards is groundbreaking, I think they can serve (as the SportsGuy might say) as a VP of common sense. It actually might help to get the fan's perspective on things; sort of a step back from what they see in practice and in games.