Most of you don't like the scenario, when players sell rolls in Raid Finder and/or roll for an item they already have, just to exchange it for an item they need in case it drops and you're stuck yet another weak without gear from the raid finder.
In the upcoming expansion, the loot system has been totally overhauled and if it becomes popular, it might even affect normal/heroic dungeons.
It already affects Quest Rewards and here's how it functions now:
Player A (Cataclysm) vs. Player B (Mists of Pandaria)
Player A is leveling a shadow priest. Upon quest completion, he is able to pick up a reward he cannot equip, for example Plate armor. I mean, you can still choose your reward, but sometimes the quest rewards no suitable items for your class.
The player can either Disenchant the item for mats, or vendor it.
Player B is also a shadow priest. Upon quest completion, he cannot choose a quest reward. In addition, his quest reward is automatically assigned according to his class/specialization, hence he automatically gets cloth armor with +INT, +STA. He will no longer get plate, leather items, nor will he get items out of his spec. (A feral druid will not get boomkin armor as quest reward, unless he isn't completing the quest as a boomkin - (needs more elaboration)
Player A: For the following quest in Deepholm (that serves as an example), useless rewards can be chosen from. (Cataclysm)
Player B: Plays a melee monk and he cannot chose a reward, but is automatically assigned one depending on his class/specialization (Mists of Pandaria)
RAID FINDER LOOT SYSTEM
How it works today
KILL > LOOT > ROLL
The boss dies, the game randomly decides which items off of the boss's loot table drop. The group rolls Need, Greed, or Pass on each item. If you were raiding with a group of friends, you might discuss who should get each item. Even if you ultimately lost, hopefully, you are happy that a friend got an upgrade and that your group as a whole is now a little bit stronger. But if you're in Raid Finder, you are quite possibly alone with a bunch of strangers. So, when you Need, you probably do, because there's no time for discussion, some of the rollers are AFK, and even if you piss someone off, you aren't likely to have to pay the social cost of doing so since you'll never see them again. The highest roller wins and drama ensues.
How it works in Mists of Pandaria
KILL > ROLL > LOOT
The boss dies, the game automatically decides who won loot, and gives those players a spec-appropriate item. Some players may still get mad, but hopefully they are mad at the laws of probability and not at the rest of the raid. Each players has a chance to win loot, independent of other players. For each player who wins loot, the game randomly assigns a spec-appropriate item from that boss's loot table. This subset contains only items that the game thinks are appropriate for your class and current spec. Notice that you aren't rolling Need or Greed. You don't have an option to Pass. (With the exception of green items). The game just says TAKE THIS.
You cannot trade the item you get. If you do not want it, you can still disenchant or vendor it.
Here's the interface of when you win an item.