Well, a lot of bloggers have thrown in their two copper on the Chill of the Throne, the 20% nerf to dodge in the upcoming Icecrown Citadel raid instance. This has brought up concerns with tanking balance, due to the imbalanced distribution for avoidance between the tanking classes. So I decided to take a look at how this is going to affect each class.
Warriors: This will be a reduction in the amount of revenge procs they get, however, the existence of critical block means that if the bosses hit softer than the ones in Ulduar or ToC, then shield block will become a significant physical damage reduction cooldown.
Druids: Dodge is the only source of avoidance that druids have, however, because of their lower avoidance, they have been blessed with more stamina and armor than their fellow tanks. This causes the increase in damage intake to actually be lower than it is for the other tanking classes. This will also help reduce the overlap in Savage Defense usage, when combined with the increased crit and AP they will gain from the higher itemization.
Paladins: Paladins are getting hit pretty hard. The 20% dodge reduction makes it difficult for a paladin in a serious progression gear set to remain unhittable with just Holy Shield up. Normally, paladins were the ones with the most to gain from decreased boss melee damage, because they could count on block value as true mitigation. This is no longer the case. We will find ourselves relying on redoubt procs to fill out the last portion of the attack table. This also severely decreases the overall value of our T10 4 piece set bonus.
Death Knights: Death Knights will be hit the hardest by the changes. They lack any form of block, so they don't benefit from the decreased melee damage, as the decreased avoidance will cause them to take pretty much the same incoming DPS as they are now, it will just be less spiky. They also suffer from a threat nerf in the form of Rune Strike. Their threat will suffer more than a warrior's because rune strike is their primary threat tool, and they don't have block to proc it, so they'll lose a greater portion of their procs. They will, however, likely be the highest avoidance tank in ICC, due to their higher parry values.
What can healers expect? Not a significant amount of change in the healing style. Damage intake should remain reasonably close to the current model, however, the spikes will be less drastic. You'll still be spammy in your heals, but more often there will actually be a need for the healing, so the overhealing will drop significantly.
This effects overall stat weights. Decreased boss damage increases the value of stamina because it reduces the gap between the magic numbers that buy you another hit between heals. It also increases the value of block value, and by extension, strength for shield users, and agility for bears. Agility in particular jumps in value for druids, because it gives them more block rating, block value, and armor. Dodge and Parry become a little less valuable, because with lower overall avoidance, more avoidance becomes less valuable. However, the value of dodge versus parry remains the same. You should not be gemming for parry in icecrown, unless you've already got more than 1.88 times as much dodge rating.
One serious gemming consideration I'd suggest for any tanks out there right now is to replace any +dodge gems with +agility gems. The increased armor will make up for the loss in avoidance, with a healthy chunk of threat baked in. While bears benefit more, all tanks will benefit more from agility than dodge.
From an itemization standpoint, I don't think this has pushed us to the point where we should abandon all attempts at balance and throw solid majestic zircons in every slot. I do think, however, that dual stamina trinkets with on demand cooldowns should be the standard for the normal progression tanking gear set. A Scarab+Heart of Iron combo will serve you well. This has, oddly enough, made Fervor of the Frostborn slightly less useless. For undergeared tanks who want to attempt to push into Icecrown who don't have access to some of these trinkets, the Glyph of Indomitability is actually more powerful the lower your overall gear level is due to the inverse scaling of armor. For primarily physical damage encounters, the Glyph will yield more effective health than the Heart of Iron if you have less than 24k armor. However, the glyph is absolutely useless on fights where the majority of the damage is magical in nature.
All said, the key to the majority of these predictions is the assumption that Blizzard will tone down the melee damage of the bosses in Icecrown. The mechanics are the deciding factor. This makes all tanks even more vulnerable to special boss atacks that do not reset their swing timer, such as Impale or Fusion Punch. The risk of having an unavoided hit line up with those abilities in an unhealably short window has increased. This has been the major threat to tanks in most difficult encounters in recent memory. Sustained melee damage is only a threat to groups with undergeared tanks or healers, and this is going to punish them the most. Most of the guilds that are already preparing for Icecrown will have no trouble with the Chill, however, the guilds that are new to raiding will find themselves getting bounced out even faster than guilds in similar positions did in Ulduar.