I would support the idea of a global help channel but it has be moderated to keep trolls from driving away the new players.
I don't like the idea of a world chat especially because we have such a large number of non-english players and a large number in each language group hates anyone who doesn't speak their language but knows enough of the other language to be an annoyance.
Also I think trading is only really viable over the forum PM system as you usually need to exchange hearth secrets unless you both have crossroad signs to a village for trading. Announcing you HS is a good way to get your village destroyed.