Lord of the Rings Online or a linkshell in Final Fantasy XI, your guild makes a big difference -- some might say too much of a difference. After all, it's awfully easy to keep playing a game you're tired of because, well, your guild still needs you.
World of Warcraft clearly uses the guild as a basic measurement of grouping, to the point where outside of your circle of friends, your guild name is often more important than your character name. It's been a long accepted fact that players who socialize and join guilds are more likely to stay in the game for the long haul. But are they too heavily emphasized? Would you rather see a greater emphasis on individual skill and accomplishments? Or do you feel that lessens your attachment to the game and your fellow players?