Thanks for writing, Ciacco! I think there are more than a few guilds who stalled out on Curator for a week or two when they first started clearing the zone. Mine did. More than anything, the fight is a DPS check and it's crucial that your "pewpew'ers" bring the pain. It's easy to look at your members' gear using the Armory and see who's behind the curve, but there are also lots of intangible skill factors that gear won't necessarily tell you about.
Problems like breaking CC, pulling aggro, or going OOM are easy to diagnose. Everybody sees the priest with the empty mana bar or the mage that gets flattened by Gruul. But to figure out who isn't living up to their statistical potential is another matter. For that, you need the raw data.
For a long time, the popular choice for obtaining such data was the DamageMeters add-on. But more and more people are beginning to realize that this add-on can do more harm than good. After trying it out once, I've never run the add-on again and I hate it when people use it as a contest. In the old days, I can't tell you how many times people would pull aggro on a Molten Destroyer -- or (much worse) Onyxia -- because they wanted to be #1 on the meters. You have to measure success and failure by the raid's success or failure, not individual achievements. It doesn't matter how many touchdowns you score if the other team kills you and all your players. (That's probably mixing metaphors, but I'm sure you get the point.)
My guild has recently started using a Web site called WoW Web Stats. One of my officers discovered this awesome tool and now we are hooked on it. To continue the metaphor, it's like a fantasy-sports stat tracker for your raid. Basically it records and uploads your combat log and generates an incredible array of statistics. For instance, it will tell you exactly how much damage a warlock did to a specific mob with each spell, including what percent were crits and how much damage was mitigated. Or you can tell whose Steady Shot hits harder on average and by how much. It will tell you how many times someone died, who killed them, and when. And who healed whom and how effectively. You even get the same data for all the party's pets and all the mobs you fight. Like DamageMeters, it helps to have multiple people gathering the data so you can recognize inaccuracies.
As far as I know, nothing else can give you such a sweeping tabulation of everything that's going on during your raids. The question is, Once you have all this information, what do you do with it? Remember that the point isn't to talk smack about who gets the biggest Eviscerate crit -- it's to figure out who isn't pulling their weight so your guild can help them improve. Blame only gets you so far. At some point you have to buckle down and work hard to fix your raid's weaknesses.
Send Scott your guild-related questions, conundrums, ideas, and suggestions at firstname.lastname@example.org. You may find your question the subject of next week's Officers' Quarters!