Players get different kinds of satisfaction from World of Warcraft. It's not just about leveling and equipment acquisition for everyone. There's role playing, exploring and crafting. And then there is the completist. Those that gain satisfaction from earning Exalted status in every faction or every piece of their class armor, even if they aren't the best for the slot.
Highlander of the Terenas server is a recipe completist. He wants every recipe in the game and one of his major hurtles is getting his hands on the ones only available to the opposite faction. So he created a list of cross faction recipes to obtain. He gives a run down on how to acquire the recipes and then recommends using the neutral Auction Houses to get it back to your main.
He notes there is one Horde recipe that an Alliance toon cannot have, Orcish War Leggings. So if you are a true completist, better roll up a Hordie.
What about you? Is there any kind of collection you're focused on completing?