There have been some changes made to two of the key components of Unholy Tank mechanics.
Namely they increased the cooldown on Bone Shield to 2 minutes, up from 1 minute and they changed Blade Barrier from a 10% increased parry chance to 5% reduced damage.
(They also did schtuff to Anti-Magic Shell, but considering that is a very situational issue and not a 'can you tank, at all' change, I haven't looked too deeply at it.)
Unholy Tanks relied on keeping Blade Barrier up to prolong the use of their Bone Shield. Bone Shield reduces damage taken by 20% (consuming one 'charge' per damaging attack, 4 unglyphed, 6 with glyph). We don't have access to a few of the seemingly 'tank specific' abilities that Frost DK's (probably the most common 'Tank' spec for DK's) have access too, Unbreakable Armor and Frigid Dreadplate. In order to get to Frigid Dreadplate (possible to do), we'd have to give up quite a bit of points in Unholy. And frankly, while 3% miss rate is nice to have, is it worth giving up some of the things that we take as Unholy because we want to be Unholy? I don't think so, personally.
In the past, we'd be popping Bone Shield like candy. In the past, keeping Blade Barrier up to increase our parry chance by 10% meant that Bone Shield stayed active until the cooldown was available.
Now, some DK's have the gear where they didn't need Blade Barrier active and could theoretically keep Bone Shield active and going without that additional 10% parry. For those of us Unholy tanks that don't have access to that gear... making sure Blade Barrier stayed active was an important element of our rotation.
Yesterday I took Keiji to Heroic UP. I was expecting it to be a bit tougher than it actually was. The damage reduction of the new Blade Barrier is a nice thing, (still miss the parry though!), that's 5% all the time, subject only to the cooldown of your blood runes. Bone Shield was being hit everytime it came up, as one would expect, but all in all... it wasn't nearly as bad as I was expecting.
So though people out there (I'm looking at YOU, Pos) keep saying that Unholy DK's are DPS, I'm thinking that I am going to keep Keiji Unholy, and Tanky.
BTW: The Red Sword of Courage dropped. If I can find another nice one-hander that will keep me uncrittable, I may switch around a few points and take the dual-wield talent in Frost (Nerves of Cold Steel) and play with that a little bit.
Normally, all these abilities would have links to WoW Head on them, but alas, a while back I was playing with my template and managed to delete the thing that let me put in WoW Head links. And I had to get that information from Pos, so I don't know how to do it myself. I shall have to pester him tonight.