The mage review has brought several new talents for threat reduction, which allows mages to perform better in raids now and generally appears to make other specs than frost more viable since you are no longer blocked by as strict a limit to your damage output on most encounters, which used to make survivability the main way to excel.
However, it appears that Blizzard has made a deliberate decision to make this threat reduction, along with the old arcane subtlety threat reduction, additive instead of the usual multiplicative threat reduction (such as BoS). I have not personally tested this but consider the information fairly credible; sources include the author of KLHThreatmeters, though I don't personally favor that Addon.

Normal threat reduction is multiplicative. This means with BoS (30%), arcane subtlety (pre-1.11 - 40%) and cloak subtlety enchant (2%), my threat would be: (1.00 - 0.30)*(1.00 - 0.40)*(1.00 - 0.02) = 41.2%.

The new arcane subtlety is additive. This would, to my understanding, make the result: (1.00 - 0.30)*(1.00 - 0.02) - 0.40 = 28,6%

I believe those calculations to be correct but I am not 100% confident in them as I have seen a lot of conflicting theories on the topic. This is what I base my further concerns on so please point out if I am mistaken.

As is shown, this significantly increases the effect of the threat reduction when stacked with other effects. In the example provided above, the 40% additive threat reduction equals ~58% ordinary threat reduction.

This means that this new threat reduction basically adds permanent BoS to Horde mages but adds significantly better threat reduction for Alliance mages.

With BoS, Alliance mages used to do 1,43 damage per threat , which is a threat limit 43% higher than Horde mages at 1,00. Now it seems that Horde mages have those stats (assuming fire or frost damage) while Alliance mages now do 2,5 damage per threat, which is a relative increase of 75% compared to Horde mages getting an increase of 43% while starting off significantly worse.

If TA totem is included, the results favor Alliance significantly less but it's my impression that Horde mages are lucky if they get to see that totem once in a blue moon. Correct me if I'm wrong. In my experience, it is fairly accurate to consider BoS permanent for all Alliance mages in raids.

I fail to see the purpose of changing this threat reduction to be additive rather than multiplicative, yet it appears to be a deliberate change since arcane subtlety is affected too.
I see the purpose of multiplicative threat reduction well enough: to keep the relative benefit of each threat reduction the same instead of letting them stack to a point where threat is no concern at all.

At the moment, it appears to me that Horde mages are as limited as Alliance mages used to be, which also restricts the viability of fire spec over frost spec, but that Alliance mages now have almost no concern for threat, except when AoE'ing. I've personally been a huge fan of aggro reduction ever since a week of traumatic Broodlord wiping ages ago but now I consider the Frostfire 8 piece bonus worthless and I am getting very careless with my threat since I mostly don't draw aggro if the tank has made a sunder and a few auto-attack hits before my first frostbolt crits for 2400+, and I have iceblock for the rare occasion when it happens.

I'd appreciate some input on whether I am correct in this and what your thoughts are on the purpose and balance of this threat reduction.

I'd appreciate input on this too, if anyone has done any testing. My impression is that it is applied after the reduction though.

It's also remarkable that the tier 2 3 piece bonus becomes better than the tier 3 8 piece bonus this way. No matter how much threat reduction I have (unless it's 100% additive of course :D), it's still useful to be able to chain rank 1 frostbolts for ~100 DPS and virtually no aggro at all. The 8 piece threat FF bonus is virtually 15% threat reduction with a bit of utility. It's of particularly little use on the opening hits though.

Speaking of threat, I'd also like to hear if anyone can confirm how crits affect threat. In my personal experience, it doesn't appear to do anything significant beyond the sum of the damage but I haven't done testing of it and last time I saw the topic brought up on the R&D, the majority vigilantly claimed that it applied a 150% modiier to the threat from crits while the minority claimed that it was just the sum of the damage. Both sides claimed to have done tests on the matter and one oddball said the threat was raised to the power of 1.5 when critting, which is impressive to say the least.

I was under the impression that all buffs listed under this category:

http://www.thottbot.com/?e=Apply%20A...at%20%28All%29

were the additive ones. The mage talents aren't listed there, but they are worded in the same way except for "...(all)" it says "...(frost)". While all buffs listed this way:

http://www.thottbot.com/?e=Apply%20A...20%28Threat%29

were the multiplicative ones. at least, that's what Kenco thinks, and I thought this was verified by a mage with fetish and bos. Also, for mage agro, you must include the 1.3x threshold for pulling agro. This lets the mage produce more damage/threat. Our nefarius mages no longer pull agro, even on broodlord. A couple of them are kinda pissed too, it's ruining their reputations.

Weird thing I ran across, arcane subtelty:

http://www.thottbot.com/?sp=12592

Is it really lowering the mana cost on all spells?

Crits don't affect aggro at all beyond the actual damage they do. This used to be different, hence the claims of 150% aggro, but testing over the past few patches has shown it not to be the case anymore. I think last time I saw Gurg mention it, it was changed in the patch after BWL's release.

With regards to mage aggro - it actually is working wierdly with all manner of things now. If you get the Fetish of the Sandreaver and activate it, with the new talents you will have 0% aggro no matter what you do. It's remarkably silly... :)

My theory is they have decided that aggro limiting encoutners, in themselves, are not fun or interesting to design around, as basically they stop people playing their classes. Hence they aren't going to introduce huge swathes of them anymore, unlike in BWL, and when they *do* introduce them, they want certain DPS classes to have an aggro advantage over others that can do similar damage but don't have tools. (i.e. rogues & mages versus warriors and warlocks).

Someone was posting on the Raid forums about Fetish of the Sand Reaver. Saying that it worked like fade, and that any agro that you generated while under the effects of it were returned in full to you at the end of the 20 seconds. Is anyone able to verify or disprove this? It would change the trinket to being quite useful for many classes to only being an AOE item, since if you didn't kill the mobs in under 20 seconds then you'd get murdered when all the threat returned to you. Especially it would screw over DPS warriors who've gotten the item.

No it doesnt work like that, and last i checked stacks fully with salv and I would assume ta as well.

Fetish definitely isn't temporary. Also, I tested the NW bonus and it is clearly applied after threat reduction.

This means that if I were to crit 2400 on a frostbolt with BoS and NW bonus, a defiance spec tank in defensive stance would need to have about 1 sunder and 150 damage on the mob to prevent me from pulling aggro.

Based on my observations so far, I think I'd have no problem going all out DPS on Broodlord with a fire spec. It's definitely not balanced and greatly reduces the value of other threat reducing effects.