I've tweaked my DK to be a Blood spec and I have to say that so far, so good. I've not have much issue with AE tanking what with DnD and the Blood Boil changes.

Also, when I am tanking heroics, the most that I tend to pull is 4 elites, so keeping aggro on them is no problem as long as I don't do something stupid like forget DnD on the pull or do too much CL.

Seriously though, my shaman team is usually LB LB LB anyways with the occasional CL and FS/Lava so I just control aggro that way.

Bosses are perhaps harder, but I also made a change from 3 elemental/1 resto to 4 elemental so I was having some issues healing anyways.

A few more days of Blood tanking and I'll have a better idea.