Exactly what it says on the tin. Whenever you deal with a forumite, either for cash or trade, you can post feedback here. The idea, however, is just a quick word of thanks to your business partner, and then details of the transfer to the rest of the forum. Things like fast/slow delivery, condition of items delivered etc. Obviously, us being a highly cerebral and gentlemanly (and lady-like) bunch, a certain amount of etiquette is expected, and the second this degenerates into a flaming groung, I'll delete it.
This thread serves the forum rather than individual traders. That way, the forum can read up on who they're dealing with, and should hopefully encourage fledgling forumites to shirk their scepticism of trading within a community.
If the idea catches on, maybe a sticky will prove useful, as I don't think trades are frequent enough to provide the thread with its own bouyancy.
Enjoy, and play fair