This is just a quick-reference set of notes which I'll probably link people to instead of rehashing all the exceptions to stacking Stamina. Nothing that hasn't been posted before. If you feel I've forgotten to mention something, please comment.
Regarding Stamina/Armor
For new content that the tank is undergeared for -- not farm content, and not low-damage content -- the Progression Tank:
-Has high Health/Armor, producing high Effective Health and more steady Rage generation.
-Does not ignore +Threat stats such as +Hit and +Shield Block Value. Coupled with Health/Armor gearing, the Progression Tank gains significantly more Mitigation benefit from Shield Block Value and more reliable Threat.
-Uses Rage Efficient talents and understands that most talents have a time and place and specs accordingly.
Why This is "Balanced"
-Platemail tanking gear is heavily weighted to Avoidance. Gemming with +Stam gems is balancing your gear, which is otherwise imbalanced.
-Item stats are not equally proportioned by Blizzard; just because an item has equal Item Level does not mean they are equally viable for tanking.
-With above in mind, Armor/Stamina combinations on items such as rings nearly always provide the a higher percentage in damage you can take than equivalent damage reduction from Avoidance stats.
-"With tanking new content, one rule is important -- it's not about taking less damage; it's about being able to take more damage."
Quick Note on Effective Health
-This term does not and cannot include Avoidance. Please read more here:
http://tankspot.com/index.php?pageid=EffectiveHealth
The above is designed around
healers, not tanks, as any gearing strategy should be. It is not the most efficient setup, it is the most
effective, and easiest to heal.
Exceptions to the Rule:
-Unusually low Avoidance always warrants more to meet basic uncrushability. Avoidance helps keep Effective Health reliably high.
-If healers run OOM on a fight, you need more Avoidance.
-Fast, low-damage mobs always favor Avoidance, such as Prince.
-Socket bonuses such as Khorium Destroyer's +3 Stamina are better served with mixed gems.
-Slow progression or exceptional/neurotic healers warrant heavier Avoidance.
-All fights have Effective Health minimums that, once safely met, do not need more Armor/Stamina.
-All content that you've already completed warrants further gear improvements in Avoidance and Threat, not Effective Health, as you've already proven you've met that standard.
Can Avoidance Tanks be Successful?
-Sure, some Avoidance gemming and gearing won't destroy all progress. As long as their item levels stay up to par with the content, they'll be able to successfully get through content. Stamina gearing is min/maxing, not a necessity.
-With the above in mind, Paladin tanks are also viable through the entirety of raiding, barring gimmick fights.
Final Note on Stamina Gearing:
-Effective Health sees relatively little gain pre-buffs moving from Karazhan to Black Temple. With the exception of T5, gains are heavier in Threat/Avoidance.
-Stamina gearing is not new to TBC -- we've been having this debate on these forums since Molten Core. It just became really obvious in Naxxramas/TBC that Blizzard was moving to favor Effective Health tanks.
Different Gear for Different Encounters
-Have a variety of gear, particularly rings and trinkets, that can be switched and customized to the fight. More Armor/Stamina is not the solution to every encounter.
-Generally, Effective Health/Block Value gear is best for handling non-raid content while wearing raiding gear.
Gilded Thorium is better than Devilshark in nearly all situations; in situations where Threat is more important, Farstriders is better than Devilshark.
Virtually any level 70 epic shield is better than Crest of Sha'tar; S2 Arena shield is better than all pre-Hyjal shields.
Quick Note on Block Rating
-As many posters correctly point out, Block Rating does not increase uncrushability and should not be stacked at the expense of other stats.
-However, Block Rating always provides a benefit in overall damage reduction. If you have some on your gear, don't sweat it.