Death knight tanking spec?

I've been doing some digging as I'm planning to level my death knight once my hunter hits 80. Against peoples judgement in I'm gonna try to make a tank out of her, until I see with my own eyes if it can be done. Although dk tanks can tank 5 mans, it is apparantly ill advised to have them tank raids. However they are good off tanks, so they say.

Now the general idea is:
frost: tanking
blood: dps
unholy: pve

At the beginning unholy was a viable tanking spec but this has been apparantly nerfed as I have only just learned. So I was *cough* wrong...

Anyways.... What are some of your ideas on tanking spec? As I have read through several forums where many say a full frost spec is not the ideal tanking spec.

I've been looking at some hybrid specs, mainly http://www.wow-europe.com/en/info/basics/talents/deathknight/talents.html?tal=2050301533000210000000000003050435103002110021000000000035002005000000000000000000000
and http://www.wowhead.com/?talent=j0E0mZGxet0x0o0oZcghh0ckL0o

Are such hybrid specs viable? Can you be a succesfull tank without going deep into any tree? I'm gonna try either way, but I would like some insight as I have never tanked high end dungeons.

Don't think I should really reply here as I don't have a DK, but tanking usually requires going in deep in one specific tree. I'm not sure of the Frost spec mentioned is like a prot spec, but that's just my 2c.

Can't really answer the DK tanking thing very well, but I do have one coment on general tanking to make.

Tanking a 5 man instance is done easily with either Pally or Warrior. This was equally applied to the old 10 man stuff, ie Kara & ZA etc. However, a Tankadin will always out-tank a Warrior tank when it comes to handling multiple mobs, there is no question about that. A warrior tank is aimed at tanking single mobs or small groups, a tankadin with a decent healer can hold aggro on much bigger pulls.
I am not familiar enough with DK specs/talents to know what their multiple-mobs-aggro-holding is like. I know they can tank single mobs, I have seen that.

To tank successfully, the toon needs to be able to take the initial aggro, then hold that threat against DPS battering at it & regain aggro if it is lost to someone critting high and taking the threat. Obviously the class/toon needs the gear/spec/experience as well, I am just referring to the ability for aggro management in this thread.
If we have a DK on Frost Spec in the guild, perhaps they might be able to answer.

I am not sure where WoW is heading with these changes to class structures. Initially , the Holy Priest was the "defined" healer (Druids & Shammys are way better now) and the Warrior was the "defined" Tank... as I say, a Paladin will out-tank a warrior in most (all?) cases of multiple mobs. Relegating warriors & priests to the DPS class for some reason.

Perhaps future patches/nerfs will change this again? Who knows....