Blood DK specs post 4.0.6, from Sconnell in the forums, who has tried to summarise where the spec discussion has ended up.
There are two main spec options for blood, both of which have room for some variation: Lichborne+2 and Desecration+2. Once the key talents are taken, how the remaining points are best spent depends on what the particular DK is needed to be able to do by their group.
Lichborne is generally considered the best way to spent the remaining talent points after investing 31 in the blood tree because it provides the biggest survivability benefit compared to any alternative. For some encounters and raid compositions, especially strategies based around kiting adds, the ability of a dk tank to apply a slow could outweigh the loss of Lichborne.
Comments on optional talents:
Bladed Armor: Bladed Armor is more valuable to Lichborne specs, because it increases the healing of death coil. In either spec, the third point in Bladed Armor can be swapped to something else if another talent is more desirable, as it does not provide a substantial amount of extra AP.
Scent of Blood: Two points is the standard for this talent. A third point will give more RP, but not much more.
Hand of Doom: This talent may be desirable for tanks who are regularly required to interrupt.
Abomination’s Might: Generally only taken by tanks who need to provide the 10% AP buff. The strength has a small but nonzero impact on survivability due to increasing parry.
Crimson Scourge: 40% extra damage to blood boil makes picking up adds easier. This talent is in the recommended Desecration build, because Desecration is usually taken for a DK tank who wants to slow adds. The free Blood Boil proc has a small but nonzero impact on survivability by generating extra RP.
Endless Winter The Lichborne spec has the option of picking up Endless Winter to reduce the cost of interrupts.
On a Pale Horse Available to the Lichborne spec if relevant to a particular fight with a moment reduction mechanic.
Unholy Command: Reduced Death Grip cooldown can be relevant in fights which involve picking up or moving adds. For the Desecration spec, this is probably a better use of points than Virulence, which now only provides a threat/damage increase.
Epidemic: The value of this talent varies depending on how often the dk has to apply diseases to keep debuffs up. Putting points in Epidemic increases the duration of Scarlet Fever. If the dk does have to apply diseases, then this talent has an effect on survivability because it means more runes are available to use on death strikes. The second point in Epidemic provides the biggest boost, because it allows a dk to alternate applying diseases with runes and Outbreak. The third point still allows for slightly more death strikes, but not as much.