Replies to forum messages are listed chronologically - newest appear at the bottom of the list.
But you can also reply to a reply, which will make a thread (indented after the original reply) into which new messages are added reverse-chronologically, newest appearing at the top of the list.
This lack of consistency is abysmally confusing!
To add to the uncertainty, the reply form appears directly under the message you're replying to, above other replies, regardless of whether your reply will appear above or below them. It's more common convention for the reply form to be positioned where the reply will appear, to give users the context of where their message will show up.
If they lose threading and put the 'reply' box at the bottom of the page (with 'reply' links on each message), that'd be like all other forums, so everybody would know how to use it.
As it is, I'm replying to Wizard's message by using the reply form that sits after my original message and before his reply, although this message will appear after his.
Paul,
The solution is easy. If the developers can add a time stamp to the forum messages, this will help to clear up who and what a person is responding to.
That's giving the user enough information to figure out what's going on, but they really shouldn't have to. If users have a forum which is an effort to use (a Ning community), or a forum which is no effort to use (somewhere else), they will choose the easier one.