World of Warcraft is a social game. Blizzard made this clear with the recent addition of the Real ID system. I myself have made use of this. Being an officer in several small roleplaying guilds on both Alliance and Horde sides of Cenarion Circle (US), I have found that there is a great bit of planning and organization required in running official guild wars. Currently, the Alliance guild I am an officer in is in a heated battle with a Horde-side guild. Both are roleplaying guilds. Both guilds (in the roleplaying sense) have similar ideas -- both are pro-Horde/pro-Alliance, respectively. One may hate the other side more than the other, but the hate is there.
These guild wars bring a certain fun dynamic to the game. Having a sworn nemesis, whether it is for a character of your creation or a friend from an opposing faction, is just a great way to enjoy the game. Plotting someone's demise, thinking of strategies to take him down? It adds another layer to an already multifaceted world. However, there are a few tips I have noticed that really help with these particular battles. Some things come in handy in a roleplaying context; others focus on fair play, so that people will want to continue to the "war" and not just want to ignore/report your taunts!