Since Diablo 3 has taken the route of real money for virtual items on the auction house, I think it will have VERY BAD consequences on the game and community. My concern is that this could (and probably will) create a lot of drama and conflicts between friends/parties. However at the time of this post I am not aware of the drop system the game will have (Diablo 2's free for all loot on the ground or WoW's roll system).
Scenario 1: You and your 3 friends worked together and managed to kill a really hard boss, an item X drops which goes for around $10 on the player auction house. You are your friends argue over who gets the item, one person gets it, everyone else rages.
Scenario 2: You are in a PuG doing some dungeon and look, its rare item Y! Item Y is perfectly itemized for you as you are class Y, and no one else in your party needs it! However this item is worth $10 on the AH, and a person ninja's it for the money.
Scenario 3: Scenario 2 keeps happening over and over again to the point where almost no one you can meet is trust worthy and the game turns into an all out ninja-fest. The Diablo 3 community begins to degrade and develops the reputation of being terrible.
Will post more later, just really tired.