Essentially, given this update, a large part of me wishes they had just held off until the beta. Right now, we just don't have enough information to make anything more than vague educated guesses about how the new rotations and abilities will play off of each other. That said, it's still worth a look at what's going down, so let's start it up and see what we can surmise.
Outbreak looks like an excellent way to quickly reapply diseases while switching targets, but in PvE, there's one major issue: We already have Pestilence. For the most part, at least currently, we have Pestilence and separate AoE rotations that will make Outbreak more or less not needed. Pestilence should have your back in most cases. That said, if we see more encounters that require crowd control, and thus where AoE is inadvisable, we may see more usage of Outbreak. Still, the one-minute cooldown will probably constrict usage in PvE.
On the other hand, it should shine in PvP, since it's harder (if not impossible) to keep a rotation going there. Just killed the healer? Hit Outbreak on the DPS, and you got enough runes to hit him with three quick frost/unholy strikes and ruin his day. Assuming our frost/unholy strikes do more damage than a combined Icy Touch and Plague Strike, Outbreak could become a very valuable burst damage tool.
While the concept of this strike is honestly sort of bad-ass, in that it's a mortal strike and yet not a mortal strike, the whole reverse Power World: Shield thing is sort of fun. The big problem is that it will probably be very niche in PvE. I would bet real money that the debuff won't stack, so only one death knight in a given group or raid will use it, and even then it will probably be weak enough that it will only be worth using in encounters where a mob can be healed.
Again, this will see a lot more use in PvP. It should especially help suppress healing in a somewhat unique way. It seems that a healer who has to deal with this has two choices: Either heal through the debuff, or dispel the debuff. Considering that dispelling is being rebalanced to be a serious choice in Cataclysm and not just something you spam, I can easily see this becoming a thorn in any healer's side and a great way to finish off an enemy by severely limiting his chance to be healed.
Once again, this is a skill that will shine brightest in PvP. By putting it on a caster, you give him a choice: Dispel it, or cast a damage spell and absorb the return damage. While there is a high chance any serious PvP caster will be able to notice this buff and simply cast a "less desirable" spell to clear it, the fact that Cataclysm spells will always be at their highest damage means at the least, he can't just quickly press a rank 1 Earth Shock to save himself.
Its usefulness in PvE will be primarily determined on how, exactly, it works. For tanks, it will be primarily extra threat, since it doesn't reflect the spell and instead gives the full brunt to the death knight, by all indications. Assuming the GCD allows it, I could see a lot of Anti-Magic Shell/Dark Simulacrum combinations for absorbing damage and causing massive threat.
For PvE DPS, it will certainly be another tool for solo death knights, but in group play, you don't get hit. That said, it's possible that the wording of the spell may save us here. Since the debuff apparently simply "copies the opponent's next spell cast," it's more than possible that the death knight can apply the debuff and cast the spell, regardless who the target is. If it does work like this, this may be the one new skill with clear usefulness for PvE DPS. If you apply the buff on a runic dump GCD and it stays up long enough for the mob to cast a spell, that's good extra damage.
But the bottom line is that two of the new abilities are almost exclusively for PvP situations, with the third being only conditionally useful, depending on whether the skill works a certain way. So while I'm sure PvP death knights are pretty excited over this stuff, as someone who focuses on the PvE game, I am mostly overwhelmed from a utility perspective. With any luck, some existing talents and skills will be revamped enough to provide some excitement for PvE death knights, though.