I doubt it.
Right. Here is the proportion of members registered between January and April that have not post a single message. Of course this figure is a bit imprecise, provided, that especially for the members registered in April, they can still come back several weeks after their registration and post.
Still, since I'm working on 8300+ members, I think the error won't be important.
So...two thirds of the registered members since the beginning of this year haven't post yet.