I'm sure originally blocking was just supposed to be additional mitigation, and as said the crushing blows thing was a side effect. It just happened to work out in a way that they were able to manipulate into a raid tanking mechanic; they've left it in for so long now that it would be class breaking to remove. Its all just speculation of course, but they seem to be using it in a positive way now.

Looking at T5 and especially T6 you should be forgetting this 85% number, aim for closer to 100%. I'm betting it is very possible to hit full crushing blow immunity without shield block in a full set of T5+ with approriate jewelry and trinkets. Even just looking at warriors in 2-3 pieces with a styleens they are looking at 33%+ shield block, that just leaves 67% to be covered in dodge/parry/miss, would be fun to play around with a crush immune tank!

Just for kicks: http://ctprofiles.net/5331728

34.37% block
23.04% dodge
16.46% parry
+509 Defense which I think is 5.6% + .04 * 159 = 11.96% miss?

So right there you've got 86% before Grace of Air, Mongoose, Scorpid Sting, Insect Swarm, Blessing of Kings, or anything else that further increases avoidance.... You can bust 100% easily. This is also rounded gear, over 13,000 hps and over 14,000 armor makes me think you can actually tank raidbosses like this and just sit there without using shield block.... You could hit 100% unbuffed if you skimp your hps but it isn't practical. Someone should do this with Tier 6 and see what they can get.

EDIT: The combined T6 difference in this particular set is + 43 defense rating (17 Defense, .68% block, dodge, parry, miss), +22 block rating (2.75% block), +52 parry rating (2.3% on new formula), -6 agility (-.2% dodge) and +1 dodge rating (+.05% dodge?) So Tier 6 would make the total avoidance 93.32 on this set I believe.

I already do that on practice. The only downside are the long strings of no hits on you thus low rage generation, 19k hp raidbuffed is enough for my healers (unless they fall asleep during the sometimes 30-40seconds long breaks in dmg flow on me). While tanking I usually dont notice these breaks in the dmg flow but on a few of our guild movies I saw my hp bar not moving for over a minute(whole duration of the magtheridon blast nova cooldown) for a few times and that got me worried a bit:P

Are you uncrushable with buffs/debuffs factored in, Highfather?

Buffs/Debuffs all the way, prior T6 its hard if not impossible to achieve passive crush immunity without gimping your overall stats too much (i.e. stamina). As I said in a previous post I swap buffs just for the sake of testing, usually I am using WF totem instead of agi one and sta food over agi food(etc etc.) so I sit at ~90% avoidance+block and still use my block skill wisely. In the not so distant future however passive crush immunity will be achievable without using buffs gimping your threat or sacrificing too much sta (even debuffs like scorpid sting) so I am asking myself if the trade off at that point will be worth it and even seen by the developers as a path that the player can choose(with all their talent/gear fiasko that is supposed to give you several options instead of being a cookie cutter as we used to).

I just finished my new excel sheet.

You can download it here:
http://dm.next-gen.org/upload/warrior_avoidance.xls

With the introduction of tier6 items it is possible to get more than 105% "avoidance" containing enemy miss+parry+dodge+block.

You can get much higher though if you keep stacking avoidance gems. Stacking block rating is a plus, you won't be crushed on the one hand but still get rage from getting hit and blocking.

Avoiding to much damage can lead into some serious rage- /threat-generation problems.

EDIT: Disregard. Looks like I'm 2 for 2 today.

The post you responded to was dated 02/16/07. At that time, you COULD use flasks+potions together.

You may wish to expand your listing of items to include some blues, such as Steam-Hinge Chain of Valor, Sha'tari Vindicator's Waistguard, Ogri'la Aegis, stat enchants on rings, etc.

There might also be of some benefit to use dropdowns for easier selection, too. That'd let people more easily whittle down gear to what they have available and how close they can get with different socket usage. In general, 1-3% crushing is what most tanks currently experience.. Thus reaching 99-100% avoidance while maintaining 490 defense, reasonable armor and HP might be of some benefit too.

I'm normally a stamina/armor sort of tank, but a few weeks ago I put together a set for passive crush immunity vs dual wielders. I've been using this set on Prince in Karazhan and it seems to work pretty well.

Recently, I got both the void reaver bracres and the tempest keep trash ring, so I decided to see if I could make a passive crush immunity set for non-dual wielders. I ended up only 6% short, so that could be made up with raid buffs/debuffs. My rule has been that I won't sacrifice anything from my stamina/armor set by adding avoidance enchants or gems to that gear.

Does anyone find this sort of set useful in 25 man raids?

Might want to check [Warriors] Shield block rating, the topic was brought up there just recently.