Lets set a few things straight. I haven't read all the posts, I don't really have the time, so excuse me if these issues have been corrected earlier. This is not a loss of 4% stam bonus, its quite more than that.
Frost Presence currently gives us 10% of our total health not stamina. Big difference, because every time you level up, you get both a stam increase and a health increase. So, if you strip all of the stamina (both from gear and stam that the character has without gear) from your character, you have a base health. This base health is currently part of the math used to determine how much we get from frost presence.
Now Blizzard is restricting this to stamina and making it only a 6% increase. This is a bit of a bigger nerf than people realize. Especially for new 80s that want to start tanking. Now, it also depends on how you are geared. My tank is stam heavy, Jewelcrafting helps me with this. I'm going to feel this nerf, but not as much as those who aren't as stam heavy. I've got almost 33k hp in a mix of crafted, Naxx 10 and Naxx 25 gear. I currently can tank XT on 10 and am not sure what else I can do. I'm going to lose 3.5k, roughly. Sure, that doesn't seem like alot, but when you discount my lack of a shield, the armor reduction and the nerf to our CDs, its just alot at once. I have those moments where I will go from full hp to nearly nothing. Every tanking DK does. That 3.5k might be the only thing keeping me up. And I'm not talking about times the boss is hitting hard either, I mean just randomly. I've got 61% damage reduction from armor, 24% dodge and 16% parry with an extra 5% mit from that one blood talent whose name is escaping my memory atm. (Alexial on Detheroc if you want to look me up)
I understand that this just means I'm gonna have to be more liberal with my CDs and to be honest I'll probably need more naxx 25 gear before I go back to Ulduar 10. Its going to be an adjustment and I'm not complaining, but I don't know who said it but this could single handledly make the best tank in the game currently, to the worst.
As for those who say that we just need to practice to adjust to the changes, forget that there are times that all the practice in the world isn't going to help you. I mentioned tanking XT and I have to blow Icebound Fort. when he has his temper tantrum. As of now, its up almost everytime it happens, so I can survive. If I don't have it up, what then, cause I don't think Unbreakable Armor is going to save me in a dire situation?
Sure, big guilds can go 'Well, our DKs aren't as good as they used to be, so we are going to use Pally's and Warriors instead." My little guild, which I run myself with my wife, has 2 tanks we normally use and sadly they are both death knights (Myself and Misacia). We have a pally tank (Lightman), but hes also our MT healer and can't really afford to let him tank as much as we'd like. So, these nerfs may put us between a rock and a hard place. I know DK tanks are OP, but I just think the adjustments should have been a bit more gradual. Too many changes at once can really hurt guilds that rely on a specific clase.
I just think we have to face the reality our guild won't be seeing much ulduar play until we can come up with some other tanks. Then again, I'll have to see how these changes corelate in-game. I just wish they wouldn't do so much at once.