My guild is going through some major drama at the moment. I'm not going to get into specifics, as I've seen some blogs descend into flamewars when someone posts something that another person feels is unfair.
However, we're up to Ragnaros, and it's this point that I think the greatest stress on a new raiding guild appears. I've seen several guilds run into trouble at this point. It really has nothing to do with Ragnaros, just that this is the point in time when the guild structure is really tested.
A guild has usually been in existence for a couple months, and for a lot of this time period guild members are proceeding in spite of any flaws in the guild structure. They are taking things on faith, that the officers will sort out flaws eventually. The officers, meanwhile, are mostly learning how to run a guild. Their solutions are jury-rigged, and fixes to mask the fundamental flaws in the initial structure. Sometimes a guildmaster is holding their guild together through pure force of personality.
Additionally, bad habits may have started in the guild, and the officers only realize that these habits are negatively affecting the guild far too late, after they have become entrenched. The problem is that most officers don't really know how to build a successful guild when they start. In a lot of ways, it's something that you can only learn by doing. And if you are an officer in a successful guild, why are you starting a new guild?
Eventually, though, faith runs out. And then a guild's core structure becomes tested. If it is good, the guild survives. If not, the guild either changes or dies.
Edit: To be clear, I don't think it's the Ragnaros fight that causes the problem. It's more that by the time you get to Ragnaros, you have MC on farm, loot is being to flow steadily.
It is at this point where deficiencies in structure begin to show up. People start wondering at percieved unfairness in loot distribution, problems with attendance, problems with rules, etc. At the start of MC, you're more willing to push through in spite of things like this, because it's new, and the high of downing bosses the first few times makes up for a lot.