Some European players recently posted topics to their forums which focused on giving constructive criticism to whoever was above them in the thread. As the draenei author of the hunters' "what does the hunter above you need?" post put it:
This isn't another "Rate my armory" thread. But rather a thread to give constructive criticism and directions for the above hunter. Like when you see a hunter in peril running around with a 2H Sword of the Bandit you could point him towards the Sonic Spear in Shadow Labyrinth. Or when a confused survivalist spends 2 of his precious talent points in Imp. Feign Death you could tell him to spend them on something more useful like Clever Traps and so on.
May the Naaru bless you all.
Not only is the idea tremendously useful, there's something about the humility and camaraderie in the attitude of this sort of post that gives me a pleasant surprise. Usually the forums (and anonymous Internet communication in general) have of all sorts of nastiness, and it's refreshing to see people using everything that the forums and the armory provide in such a cooperative way.
I found "what does the player above you need?" posts for Hunters, Warlocks, Rogues, and Warriors. If you have found similar forum posts for other classes, or posts with remarkable constructive criticism of another sort, please mention them in the comments below.