Blizzard released a post on the stat changes that have gone live with Patch 4.0.1.  Here are the changes: [Source]

We’ve previously unveiled some of the stat changes that are coming with Cataclysm, including stat alterations, stat removals, or changes to how they’re obtained. This is an update to that preview intended to explain the actual changes and to detail what everyone will be seeing on their characters.

Stat Changes

Stamina – Due to the assigning of Strength, Agility, and Intellect, non-plate wearers have more Stamina than before. Health pools are now much closer between plate-wearers and other classes.

Spirit – This stat should only be found on healing gear. Non-healing casters have other systems in place to regenerate mana.

Intellect - Intellect now grants Spell Power and increases your Critical Strike chance with spells.

Haste – Haste should now be more attractive for melee classes by allowing them to recover resources such as rage, energy, and runes more quickly. Our intention is for Haste to let you “do stuff” more often.

Parry – Parry provides the same avoidance as Dodge, and you’ll receive a percentage of your strength as Parry Rating.

Mastery – 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.

Armor – The amount of bonus Armor received per stat point on items has been drastically reduced, and Armor is no longer given by Agility. In addition, Armor now better mitigates differences among Armor types so that protection from mail, leather, and cloth is much closer to that of plate.

Resilience – This now only affects damage done by players and their pets. It will not impact crit chance, crit damage, mana drains, or other such effects.

Removed From Items

Attack Power – This stat is rarely present on items, although it is derived from other stats. Strength and Agility, which are present on items, 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.

Block Rating – Block has been redesigned to scale better. Blocked attacks will simply hit for 30% less damage. Block Rating is no longer given out directly as a stat. Instead, Mastery for Protection paladins and Protection warriors increases the chance to block.

Spell Power - Spell Power is no longer present on most items. Instead, as mentioned above, Intellect now grants Spell Power. One exception is that caster weapons still have Spell Power. This allows us to make weapons proportionately more powerful for casters in the same way they are for melee classes.

Armor Penetration – This stat is no longer present on items. Armor Penetration still exists in talents and abilities.

Shield Block Value – There are some effects that increase the Block value by a percentage, but this does not exist as a stat.

Removed From the Game

MP5 - This stat no longer exists in the game. Holy paladins and Restoration shaman have been redesigned to benefit from Spirit.

Defense – Defense is now removed from the game. Tanking classes will become uncrittable versus creatures by shifting into Defensive Stance, Blood Presence, or Bear Form, or by using Righteous Fury.

Spell Ranks - Spell ranks now cease to exist. All spells have one rank and will scale appropriately by caster level. The levels at which you can learn certain spells have been changed in order to fill in some of the gaps, and there are many new spells to learn along the way as well.

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.

What Else You Should Know

Combat ratings – Ratings are much harder to “cap out” at maximum gear levels. Ratings are steeper in Cataclysm, and creatures in later tiers of content will be harder to hit or crit, similar to how level-83 mobs are harder to hit or crit than level-80 mobs.

Reforging - This new itemization customization feature allows you to partially change the stats on an item. You can reduce the value of an existing stat on an item, and add an equivalent amount of another stat that was not already present on the item. This makes it far easier to reach important thresholds like the Hit Rating and Expertise Rating caps.