Death Knight tanking is totally, totally different than warrior tanking. There are far less buttons to hit, for one, and all 3 talent trees have different strengths and weaknesses. But for the sake of clarity and because the Blood tree is becoming the dedicated tanking tree come Cataclysm, all of my post about my DK will be from the point of view of a Blood tank.
AoE tanking, is much much much easier for a DK, in any spec that is played (notably easier for Unholy tanks, but you don't see too many of them around). An AoE rotation is very simple Death and Decay, get your diseases up, pestilence, and if you're in a pinch for some snap threat, Rune Tap then Blood Boil. Then, you wait. A long time. There seems to be alot of "do nothing" time as a DK tank waiting on the runes to regen. Now from my understanding, Blizz is changing how runes regenerate in Cataclysm. I'm not in the beta, so we'll see how that works out when it's released. DK's also seem to be pretty restricted by the GCD. I've had a few good DPS pull aggro off me before my diseases are even up, simply because i'm restricted by the GCD.
Another note, Blood tanking is -excellent- for single target boss tanking. In terms of threat generation, Heart Strike is probably the best threat generation attack out of all 3 trees. But, since it is pure physical damage, an armor reducing debuff from a fellow raider is desirable. The blood tree also is also full of delicious talents that contribute to effective health, which seems to be the end-all for raiding.