As you may or may not be aware, one of the things coming with Cataclysm is guild ranking.
With that, there are guild achievements and guild experience to be earned. And as your guild levels, there are various perks available to guild member. There is also guild reputation, which is probably to discourage guild-hopping.
Overall, it sounds pretty neat, although I hope it isn’t overly difficult for smaller guilds like ours to advance. But I’ll guess we’ll see.
What are your thoughts on the guild advancement/achievement system?