An interesting thread has cropped up on the official World of Warcraft forums, asking the question of "Has TBC broken your guild yet?" You can find the thread here.
Personally? I don't think so. MMOG's are a volatile beast when it comes to how the games affect its players, and expansions compound this a great deal. People come and go, and changes in the expansion(such as the raid cap being lowered from 40 players to 25) can really factor into the way a guild changes. I don't feel 'broken' is the correct word here.... I would go more with 'change.' How has TBC changed your guild? That seems like a better question, and really sounds better too. You don't want to kill people's morale when there's no reason to.
For veteran MMOG players, like myself(I personally have played them for close to 7 years now), it's not really anything different. We've seen the way expansions change games, sometimes for the better, sometimes for the worse. World of Warcraft's first expansion hasn't changed much of anything for my guild, or my outlook of the game in general; I still feel it's an excellent game, and they made a step in the right direction to improve upon player quality with their focus on designing challenging content for smaller numbers of people(Heroics and Karazhan spring to mind instantly).
The biggest change I've seen so far in the expansion is the fact that it's brought a lot of the members of the guild even closer together. We spend a lot of time running instances, something we haven't done in over two years(and even then we didn't do it all that much before jumping into the raiding game - it simply wasn't required to the extent it is now), as well as helping each other out with various trade skill needs to prepare ourselves for the 25-person raid zones.
Now, for players new to the genre, with World of Warcraft as their first game, major changes like were made in World of Warcraft: The Burning Crusade can certainly be jarring. That said, it's not the end of the world; guilds will always go through turbulent times - whether through members coming and going(which is common-place in the MMOG genre), or overall changes to the guild hierarchy and its policies for various facets of the game you're playing - it's important to remember that you're in a guild for the people around you, not the items those people can get you.
So without rambling on for paragraphs upon paragraphs(believe me, I certainly could on subjects like this), I think this is a good time to pose the question to you, the World of Warcraft Community; not in a "the sky is falling" approach, but rather to be curious about what has changed for you personally, and your guild. And with that: How has World of Warcraft: The Burning Crusade changed your guild?