Following up on the post Eyonix made in regards to stat changes in World of Warcraft: Cataclysm, I have decided to break up his post into different articles here for easier understanding. Here are the stat changes in relation to how it will affect gear. What Eyonix said will be in italics, and I will put in bold key changes:

What’s Staying?

1. Stamina - Because of the way we will be assigning Strength, Agility, and Intellect, non-plate wearers will end up with more Stamina than before. Health pools will be much closer between plate-wearers and other classes.


2. Spirit - Come Cataclysm, this stat should only be found on healing gear. Non-healing casters will have other systems in place to regenerate mana, and we are designing special solutions for Elemental shaman and Balance druids who often share gear with healers (more on this below). Raid buffs that currently boost Spirit (such as Blessing of Kings) will only boost the primary stats of Stamina, Strength, Agility, and Intellect. We are also likely changing the five-second rule and other quirks of the current regen system.


3. Intellect - Intellect will now grant Spell Power. Intellect will also provide less mana than it currently does.


4. Haste - Haste will become more attractive for melee classes by allowing them to recover resources such as energy and runes more quickly. Our intention is for Haste to let you "do stuff" more often.


5. Block Rating - Block is being redesigned to scale better. Blocked attacks will simply hit for 30% less damage. Block rating will improve your chance to block, though overall block chances will be lower than they are today.


6. Parry - Parry no longer provides 100% avoidance and no longer speeds up attacks. Instead, when you parry an attack, it and the next attack will each hit for 50% damage (assuming they hit at all). In other words, Dodge is a chance to avoid 100% of the damage from one attack, Parry is a chance to avoid 50% of the damage from two attacks, and Block is a chance to avoid 30% of the damage from one attack.
 

7. Mastery(New Stat!) - This is a new stat that will allow players to become better at whatever makes their chosen talent tree cool or unique. It's directly tied to talents, so what you gain from improving this stat is entirely dependent upon your class and the talent specialization you choose. We’ll talk more about specific Mastery benefits in the future.


8. Armor - The way Armor mitigates damage is not changing, but the Armor stat has been rebalanced to mirror changes to the armor curve in Cataclysm. As a result, bonus Armor will go down slightly overall. We are also changing the mitigation difference among armor types so that plate doesn’t offer so much more protection than mail, leather, and cloth.

9. Resilience - This will only affect damage done by players and critical damage done by players. It will not impact crit chance, mana drains, or other such effects.


10. Strength, Agility, Hit Rating, Expertise, and Critical Strike Rating - These will all still appear on gear as well. Aside from situations mentioned elsewhere in this list, in general these will function similarly to how they do now, though the details -- such as how much Hit Rating you might need to effectively combat high-level creatures (more on this below) -- are likely to change.

What’s Going?

1. Attack Power - This stat will no longer be present on most items as a flat value, though it will still show up on some process. Strength and Agility, which will be present on items, will grant the appropriate amount of Attack Power (generally 2 Attack Power per point of Strength or Agility) depending upon which stat a particular class favors. Agility may provide less Crit than it currently does. (Basically, Attack Power will be embedded into Strength and Agility)

2. Spell Power - Spell Power is another stat that you'll no longer see present on most items. Instead, as mentioned above, Intellect will grant Spell Power. One exception is that caster weapons will still have Spell Power. This allows us to make weapons proportionately more powerful for casters in the same way they are for melee classes. (The only item you will see Spell Power on are caster weapons. Intellect will be the primary source of spell power.)

3. Armor Penetration - This stat will no longer be present on items. Armor Penetration will still exist in talents and abilities.


4. Shield Block Value - This stat will no longer be present on items, since the amount blocked is always proportional to the amount of damage done. Talents and other effects might still modify the damage-reduction percentage from 30%, however.

What’s REALLY Going?

1. MP5 - This stat will be removed from the game completely. Holy paladins and Restoration shaman will be redesigned to benefit from Spirit.


2. Defense - Defense is being removed from the game entirely. Tanking classes should expect to become uncrittable versus creatures just by shifting into Defensive Stance, Frost Presence, Bear Form, or by using Righteous Fury.


3. Spell Ranks - Spell ranks will cease to exist. All spells will have one rank and will scale appropriately with level. The levels at which you can learn certain spells are being changed in order to fill in some of the gaps, and we will be introducing some new spells to learn along the way as well.


4. Weapon Skill - This stat will be removed from the game completely. Classes will start with all the weapon skills they need to know and will not need to improve them.

More info breakdowns on the way with other changes in Cataclysm!