The matter of having forum posts treated as messages has been really badly executed. This is particularly noticeable on the (admittedly high traffic) moodle.org site.
1. The barrage of popups saying "you have n new messages" is, at best, an annoyance.
2. If you mean forum posts you should say forum posts to avoid confusion - "you have n new forum posts" AND/OR "you have n new messages" would be better. It would be even better if it could be restricted to forum threads you actually participated in (a long time coming).
3. Having accepted the link to the new 'messages' all you get is a big list of usernames. I'm not sure what purpose this is supposed to serve or what the intention was. It seems the most useless option (for forum posts). You actually need to know what the discussion was and/or what forum it was in.
4. Having accepted one of the 'messages' (if you know to select the mysterious icon that is) you get the recycled message UI which implies a conversation between yourself and the message poster. This is clearly just wrong - surely you should go the the actual forum post or the UI should be much more clear that this is a forum post not a proper message.
Sorry to sound so negative but this seem thoroughly broken to me.