The sheer number of players in WoW means that you'll run into a variety of people while levelling and otherwise passing the time in-game. Currently, the in-game feedback mechanism is one-sided, and limited: if a player is unbearable, then they can be welcomed to your /ignore list, but if they're worth remembering then they get a place on your friends list.
Depending on how you play, these lists may be sparse or full, but if you're anything like me then you wish there was something more to it: the ability to see what others think of a player, and the ability to help others stay away from bad players or gravitate towards good players.
This soapbox piece over at Gamasutra goes into the ins and outs of character rating systems as applied to MMOs. It brings up some important points; people will try to game the system, by creating characters solely to leave ratings, and there should be further requirements such as having to group for X minutes. Also, there would have to be a RP explanation for ratings, and a decision would have to be made over whether to use user-specific or character-specific feedback. The former means that everyone can be forewarned you're a jackass; the latter means you can RP a jackass without harming your other characters.
Personally, I'm not sure I want a disgruntled group member harming my reputation for life just because we disagreed on the best way to heal -- nor do I want the person who called me a n00b because I wasn't specced the way he wanted to have much of an impact on my ability to find instance parties. On the other hand, I'd definitely like to be able to avoid people like that.
It's unlikely a system like this could be shoehorned into WoW by Blizzard, but it's certainly fair game for an addon, if enough players would install it.
[Image credit: Fan art by George Tutumi]