I have a love/hate relationship with ElitistJerks, the kings of theorycrafting. If you are looking for numbers on something, they provide some of the best resources. If, however, you are looking for tips on how to handle various situations better, or how to become a better healer, they are useless. They will throw numbers at you and ridicule you if your numbers are not what they consider ideal.
The thing is, it is very rare to find yourself in a raid mix and situation that is ideal - that's why it's CALLED ideal. The numbers they provide always have basic assumptions attached to them - such as who else is in the raid with you, what buffs you have, that sort of thing.
But what if I *don't* have a resto shammy with me? What if there are no druids available for an innervate? What if we don't have a shadow priest? Surely all these things would be ideal, but it is not practical to always assume this will be the case.
The way you should gem and enchant your gear, the talents you choose, the stats you prioritize should all take your fellow raid members into account of course. As I've said before, raiding is about synergy, not about individual perfection. At the same time, the numbers and theorycrafting provided by folks like the ElitistJerks will very rarely actually properly apply - because it is very rare that the average raider will ever meet all the conditions assumed by the EJ calculations.
The problem is, people get so hung up on tiny little numbers that will potentially boost their stats by such infintesimal amounts, that they completely forget to balance themselves.
Theorycrafting and the math that goes with it gives people the impression that there is really only one "best" way to do something - the way that maximizes the numbers used in the calculation. But the average raid is a lot more dynamic than I think people like to admit. Changing things up is how people learn new fights, conquer new material. If I couldn't keep people alive with loads of crit rating, maybe I'll try it with tons of haste and see if that works better. And people heal differently. So if you don't gear yourself for how YOU heal, and instead try to gear according to how EJ insists you should heal, you are not doing yourself or your raid a favor.
Does that mean theorycrafting is stupid? Not at all - much like meters, it is a useful tool to help you improve. Use that theorycrafting to make decisions between choices you have in front of you, between items you might pick up. But don't let the theorycrafting of others dictate everything about your character, because especially for holy priests, there are a lot of flexible variables.
If you are new to a class or role, reading up on theorycrafting and scanning through the EJ priest forums is a fantastic idea. Had I not done this, I would still be stacking spirit and ignoring intellect. Until you find your niche, until you train your reflexes and trigger fingers properly, it is not a bad idea to default to the suggestions of the more experienced among your class, and those with the math skillz to explain it all.
But, once you get a handle on the basics of your class, and once you start to develop your own rotations and habits and strategies, stop depending on the way others choose to gear, and start figuring out what works best for you. There is an awesome discussion along this line of thinking from the Penance Priest for those Disc Priests who are at the stage of the game - you've got the basics down, now you are ready to personalize your style and priorities a bit. There are still wrong answers, a la agility for Priests and all sorts of degrees of less obvious fail. Every healing priest (probably all priests period) need to pick up Meditation, for instance. It's really not optional. But just like how there are multiple wrong answers, I assure you friends, there are also multiple right ones.
From Poptisse, whom I absolutely adore, and for whom I have tauren-loads of respect:
"What people have to understand is the basics of raiding. When you gem and enchant your gear there is more then 1 aspect to look from. [...]Gems and enchants should always be decided upon a wide perspective of your raidsetup. My guide isn't a bible, neither is EJ guides."