WoW, WAR & Persistent PvP

Tobold spotted Keen and Graev compare WoW's and Warhammer Online's PvP. I've also touched upon the issue while dicussing persistence, but Tobold does point out that if you give players immunity due to barriers such as factions, someone's going to abuse it.

EVE Online, on the other hand, has no such thing as predetermined factions, so players are free to punish former teammates as they please. The plurality and fluidity of player alliances ensures that no group has uncontestable supremacy, which keeps the game interesting.