Interesting stuff!

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.

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.

These two together are interesting: it seems like the effort is being put into tank’s time to live deriving less from health and armor mitigation (aka effective health) and more from other stats. I’m not sure how I feel about, or at least understand, declarations like stamina and armor will be similar across tanks and non-tanks alike. I suppose reforging and enchants/gems will expand that gap, but it’s sort of weird.

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.

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.

Makes sense, they were talking about bringing Block down so you couldn’t go through a heroic with like no damage while a Druid or DK would be dealing with a lot more pain.

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.

This is the most interesting change, I think, and definitely the most unexpected. A smart idea to change Parry so it isn’t just a carbon copy of Dodge. I like this implementation, although I’m assuming that damage reduction is just applied to the next physical melee attack.

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.

Operative phrase here being “versus creatures.” So a Ret or Holy Paladin can’t slap on RF and be crit immune in pvp. Great idea, and quells many concerns when this was first floated as a change to RF a few weeks ago.

Finally, they sum up our 4.0 gear adjustments as:

If you are a tank (druids excepted), expect to see:

No more Defense on gear. Existing Defense becomes Dodge, Parry, or Block Rating.
No more Block Value on gear. Existing Block Value becomes Block Rating.
You’ll have as much Stamina as you’re used to, though you may notice your tanking plate has a bit less Stamina than a comparable piece of DPS plate, since we tend to take the gem budget out of your most attractive stat.
Bonus Armor on gear will go down slightly.

Sounds to me like Cataclysm will change tanking to be less EH-centric and more diversifying out toolset so avoidance (as we now know it) along with the new Parry and Block mechanics are worthwhile in a raid situation. Awesome.