Ok, i specced my rogue to 18/43 last week hoping the daze effect from blade twisting would work on bosses, and thus give the tanks more threat due to heroic strike, and hunters more damage with steady shot.
Sadly it seems they list as immune.

I recall someone saying piering howl works on bosses to apply the daze effect.
e.g. : the boss gets dazed, but is immune to the slowing part of the debuff.

Rogues, hunters, warriors have an option, spell or talent to daze mobs.
but,, it seems not all of them work, perhaps it does on some bosses?

I'd love to share some test on this. where to start?

start with testing it on immune mobs to see if they get the icon daze under their debuffs. afaik tahts whats happens with piercing howl, you get the immune msg but it gets up on anyway without the daze effect (just the debuff daze witch is enough for steady shot and HS).

btw, you dont need blade twisting and i dont recommend hunters going conc barrage for hte daze proc, a warrior using piercing howl every 6 sec is the most efficient way to apply it in a reliable manner.
preferably a debuff bitch arms warrior who aint gonna do any dps anyway worth mentioning.

Nightbane didn't show the icon.
Wednesday i'll keep an eye on my combatlog @ maulgar and gruul.

Im fairly certain the daze effect giving improved damage is for pvp only. Or at least for none raid bosses in pve.

On a related issue, what is considered "Daze" at all?
I see Piercing Howl to be a snare with Apply Aura: Mod Speed Slow, Blade Twisting leads to Dazed (obviously), which is also a snare with Apply Aura: Mod Speed Slow.
If we look into Apply Aura: Mod Speed Slow, we see a whole lot spells having this effect, including Crippling Poison.

So, what is considered a Daze and what not?
I could not find any references under Heroic Strike.

The mobs get a "Dazed" debuff if they're dazed. Works on some mobs, doesn't on others. I haven't really put any time in looking into what kind of mobs can and can't be dazed.

I'm suspecting the latter.
I'd love to hear the results of others in this regard. (wonder why blizzard nerfed this, or whether it's a bug?)

My guess is someone thought it too OP to add increased melee damage from Piercing Howl.

I've seen the same thing reported here, all the skull-level bosses in KZ/Gruuls that used to be affected by PH have been throwing immune messages since 2.1. Gave our other group quite a surpise on the Wolf event, for sure.

it mostly affected hunter dps anyway since no dps warrior in their right mind will spam HS. i guess having constant +175 dmg on SS for hunters would be very overpowered. BM hunters dps would skyrocket which is already highest. a sad but understandable change.