Bukkit

My suggestion is that players in a certain world can use only the channel defined for that world. Not even global chat.
This would be useful for adventure maps in a server, so other players can't spoil the adventurers fun by telling them sollutions to their riddles.

Could you possibly explain a bit more in detail?

Well it could work by automaticly forcing players to leave all(or specified channels in the config) channels when they travel through a portal to the new world. The world would have it's own chat channel defined by the main ChannelChat plugin, and players would automaticly join only that channel.

If they attempted to join the global chat, it would deny it.

That's how I imagine it would work, but perhaps you can come up with better sollutions. I'm not skilled in writting plugins and don't know what all is possible :)

I'll think about it, thanks for the suggestions!