Taurenia, my Level 72 Unholy Death Knight on EU Dragonblight Horde. This is a screenshot of me in my tank gear (mostly crafted Cobalt plate). I'm still crittable as I have only 457 defense but I don't think it matters much considering how easy early dungeons are.
I've specced 5/5/X
http://www.wowhead.com/?talent=j0xZ0xZfg0I0foMcqMcsup so that I can level efficiently as well as tank any instance on the way. I find questing faster and more fun as you get to do all these exciting quests and read up on lore, so I haven't tanked much other than Nexus (which was easy).
Jumping up and down is silly, but it really helps on Keristrasza, lol.
My rotations are as follows.
DPS: IT, PS, SS, SS, BS, BS. RS if I dodge/block/parry, UB if I have the RP and DS if I need to get back some health. On AoE, I make sure I stick in Pestilence after IT and PS.
Tanking: DnD, IT, PS, Pestilence, and spam DS. UB and BB as soon as they are ready. I rarely use SS and BS here. DS is amazing, can crit over 2k meaning healers can afford to slack
The only thing I miss though after playing a Paladin is an AoE taunt, but providing the DPS don't do anything stupid, a quick DnD should be enough to get them back to me in addition to Dark Command and Death Grip.
Overall, I'm loving this expansion. I was originally going to start an Alliance DK and start with Howling Fjord, but then I rode into Warsong Hold and the music just decided it for me; I will start in 'Boring' Tundra instead. The music that blares out in Dalaran too gives me goosebumps. Then there are the quests, so much variety and much lore, not the usual '20 X slain' or 'gather 10 X'.