Player vs. Player in World of Warcraft

RPGVault has dished up yet another World of Warcraft feature, this time with lead designer Rob Pardo discussing the game's player vs. player implementation, incentives, and rewards. An excerpt to follow:
One very important motivation in designing PvP into the World of Warcraft was to make it feel like Warcraft. Warcraft - starting back in the day with Orcs and Humans - was about the war between Horde and Alliance. We have expanded the Alliance and Horde to encompass more races within each side, but it's still, at its core, a game about the conflict between the two factions.

We designed our world to reflect this tension and to create situations that bring players into conflict with the other side. Our quests encourage you to attack the NPCs of the opposing faction. We also set up our zones with conflicts already ongoing between the two sides, and then ask you to participate in those conflicts. For example, in the Hillsbrad zone, there is both a human town and an undead town, and the undead town has a series of quests that ask you to go to an Alliance village and defeat human peasant NPCs. We feel that is a great way to remind the players that a war is still raging between the Horde and Alliance. It gives both sides reasons to dislike the other players. An undead player in Hillsbrad is made to feel like the humans are his enemies, and vice versa.