@Jacoobus:
Haki is a power that relies on the user's vitality/life force, it makes sense that WB's Haki isn't what it used to be. When he got stabbed by Squardo or had his face taken off are examples of how he'd weakened. I don't think Haki would block those attacks, but if he was able to use CoO effectively he should have seen them coming and been able to dodge.
Looks like I missed the debate, but seems to have settled on Whitebeard having haki, which I would say is the reasonable supposition; I also think this post gives at least a decent reason as to why we didn't exactly see much evidence of a high level of haki mastery out of him during the war.
I find the last part of the post a bit interesting, though. To me, CoA is at this moment the most ambiguous of the three colors. CoO is more or less straightforward, unless you start getting into issues of what would happen if both combatants were using it against each other; and CoC, at least in terms of its known applications, is quite simple as well. CoA, on the other hand…
First, there's the defensive aspect. On the one hand, it's true, as far as I can recall, that we've never seen someone use haki to just sort of 'tank' an attack. On the other, it's clearly possible to imbue it into things: for example, Shanks blocking a magma-fist with his sword seemed to me a clear application of armament haki. That said, if it's possible to imbue it into random objects, then I can't see why it wouldn't be feasible to simply imbue it in whatever part of your body you wanted, and therefore simply be impervious to attacks so long as you were 'defending' the appropriate spot, which should be easy enough with usage of CoO.
The only thought I could have as to why this wouldn't be the case would be that, as far as I can think of, all known cases of using CoA as a defense have involved a sort of active 'repulsion', or motion of pushing away. In general, this takes the form of the palm out motion, but the case of Shanks blocking Akainu, if you take it to be CoA as well, would also fit under that same general description. In that case, defensively, you could look at armament haki not so much as an impenetrable shield, but more of an ability to push or deflect attacks away.
On to the offensive side of it... Arguably the most major use of it offensively is the ability to 'hit a devil fruit user's true body'. Hence, why haki users have been able to cause blunt damage to Luffy, and a work-around for having to come up with ridiculous elemental weaknesses for every logia fight. Fair enough conceptually; however, its actual uses in universe have left me a bit confused, notably when it comes to attacks with a blade.
The first example was when Raleigh attacked Kizaru with his sword, to prevent him chasing the fleeing Strawhats. This stopped him, and led, if I recall correctly, to a small slash on his cheek. On the other hand, Whitebeard pulled a similar move against Kizaru during the war, keeping him diverted from Luffy. I'm forced to assume CoA was employed here as well, as it did succeed in stopping him; I would assume Kizaru would have ignored it entirely otherwise. However, again to the best of my recollection, Kizaru suffered no physical injury from this.
I suppose you might argue that Kizaru is a special case. Both those examples were while he was turning to light, about to move, and hence even hitting his 'true body', you might argue that he was so diffuse at those moments that what seemed like rather extreme attacks simply didn't end up causing that much, if any, damage. However, you then later have the division commanders attacking Akainu. You see them land hits on him, and he complains that he is now facing haki users. To me, this gives the impression that he comes to this conclusion since he has actually been 'hit'; however, the gashes on his body end up leaving absolutely no effect, as they would if they had been any normal attack on a logia user.
So... that post went on a while, but basically, assuming everything we have seen so far has been consistent, and not in error -- and assuming my various interpretations aren't entirely off base -- then I feel like CoA, which will arguably be the most important version of haki in the future, still needs quite a bit of explaining and clarification to understand exactly what rules it is it follows.