There are a few points I'd pick on:
1.) Toughness. Don't leave home without it, it's multiplicative with Frost Presence and worth a LOT of armor (~3.5k for me).
2.) Imp IT is very very valuable for survival, unless you're expecting to have a warrior with Imp Tclap keeping the debuff up. DK's can do it better though, and the boost to IT damage is very nice for your threat.
3.) Mark of Blood and Vet of the 3rd War are great talents for tanking, and they can make your tanking gear look even sexier, but you always have to beware of getting into Blood just for those buffs as they tend to provide less in the balance than you lose from other trees, though it's a survival buff and you're losing threat from the other tree, that's usually why people do it.
4.) The interesting thing is that your spec is otherwise about 90% threat in the threat/survival balance, so if anything I'd expect you have heavy single target threat, somewhat weak aoe threat, and would be rather low survival on the scale, though you may notice it less with your gear depending on what you're tanking.
5.) Necrosis and BcB make for a very vicious compounding dmg, but it also increases your vulnerability with dmg taken from parries (Blood-caked strikes are parriable). Again, it may not be a big deal, and you won't see it in 5-mans ever really, but raid bosses will hurt you more.
I think the big weakness of the spec is simply that it doesn't support a concise focus or easy rotation. How do you play it?