Let's talk talents.
This is now the dedicated tank tree. We gain Bone Shield from the old Unholy tree, Toughness from Frost, a -10% damage debuff added to Blood Boil, Crit Immunity from Blood Presence (bai bai def cap), free Icebound Fortitude, reduced CD on Strangulate, and finally Crimson Scourge; in addition to buffing Blood Boil's damage, if you use Plague Strike (since a single Unholy rune isn't super useful in an AOE tank situation) and the target is already infected with Blood Plague, your next BB is free. Additionally, Rune Tap is now improved by default, and a number of talents now cost less.
We lost...almost all of our DPS talents, as to be expected from a tanking tree. We retain Abom's Might to provide a raid buff (beyond horn), and remain a cooldown-focused tank. All in all, I'm generally pleased, although there honestly weren't that many changes to Blood from a tank perspective. Bone Shield isn't bad as long as it's viewed as another short cooldown instead of something to try and maintain for a damage buff.
Lastly, Blood's Mastery is Blood Shield: whenever you use Death Strike, you gain a shield that absorbs damage equal to 50% of the healing. I like this a lot, as it ensures you get the most out of your DS healing rather than risk some (or all) going to overhealing.
Frost gains On a Pale Horse (+mounted speed) from Unholy, a 4% increased physical damage taken debuff, a late-tier talent option for 2h Frost, and Pillar of Frost: essentially a tweaked Unbreakable Armor; it still increases Str by 20%, but rather than improve armor it now prevents against movement effects such as knockback. This fits the fact that Frost is now a dedicated dps tree; there is no longer a need for survivability talents. One final change of note is that Howling Blast now (again) has no cooldown.
In addition to losing a ton of passives, Frost loses Acclimation (magic resistance), Toughness, and Deathchill; the latter is the only DPS loss, as it was a free crit for your next Icy Touch, Frost Strike, Howling Blast or Obliterate on a 1m cooldown. Beyond that, the tree lost nothing interesting that was of any use for DPS. Frost's Mastery is Frozen Heart, a simple 20% increase to all Frost damage done. All told, they've done pretty well with Frost imo. Removing the cd on Howling makes the build more AoE friendly, while adding a 2h option (while maintaining dw) gives the tree a lot of versatility.
A lot of fun new stuff in the Unholy tree (which is good considering how many of it's old talents ended up in Blood and Frost). First off we've got Resilient Infection, a PVP talent that refreshes your runes when your diseases are dispelled. Next is Runic Corruption, which changes your Runic Empowerment to grant you +50% rune regeneration (instead of simply activating a random rune). Unholy also gains Hysteria, which is now renamed Unholy Frenzy. The final two new Unholy talents are ghoul related: first is Shadow Infusion, which applies a stacking (5x) 10% damage buff on your pet every time you cast DC. Next is Dark Transformation, which consumes all 5 stacks of Infusion to transform your pet for 30 seconds. These two really flesh out the role of the Unholy DK as the Warrior/Necromancer hybrid.
Gone are Bone Shield, On a Pale Horse, Wandering Plague, Crypt Fever/Ebon Plague, and a ton of passives. Surprisingly, Antimagic Zone remains (as does improved AMS), retaining the iconic PVP utility of the Unholy DK. The Mastery for Unholy is 20% increased disease damage; this is as unimpressive as Frost's, but with the rest of the changes it's hard to be too disappointed.
That wraps up my overview of the DK Talent changes coming for Cata. As with all unreleased content, this info is subject to change at any point. If that happens, I'll keep you guys posted.