Gift of Arthas

The only good use of Arthas' Tears is the Gift of Arthas. If you're running a melee heavy raid, it really does shine. Also, the 10 SR helps on certain fights. BWL's drakes, Nef, Emperor Vek'lor.

It does stack with the rogue Hemorraghe ability.
It is a disease and as such applies to magic immune bosses.

A quick summary of it's damage:
5 warriors, 5 rogues, 2 pallies (regening via seals) at any given time.

2 Prot warriors: 4 strikes every 3s. X2.
3 DPS warrios (assuming MS for conservative math) 2 strikes every 3s. X3

5 Rogues: 3 strikes every 3s. X5
2 Paladins: 1 strike every 3s. X2
That's 8X4X2+8X2X3+8X3X5+8X1X2 = 64+48+120+16 = 248 damage every 3s = 82.66 (repeating, of course) DPS.
This ignores hunters who DO get a bonus from GoA.

In short: Imagine if you had a mage afk and wanding, thats the amount of extra damage this gives you.

There's more to it than just the numbers posted above.

1. The +8 damage is post mitigation. Assuming an easy standard of 50% melee mitigation on any boss mob, it actually equates to what is like a +16 damage sharpening stone on all your melee/ranged weapons.

2. Rogues hit more than 3 times in 3 seconds.
2 Sinister Strikes
2 Off-Hand Strikes (OH usually 1.4 to 1.6 on Rogues)
1 Main-Hand Strike (Usually 2.2 - 2.6 MH speed on Rogues)

Prot Warriors Generally hit 2-3 times in 3 seconds.
1-2 MH weapon Swings
1 Revenge/Shield Slam

MS Warriors is 3 per 3 seconds
2 MS strikes
1 White Weapon Swing

DW Fury Warriors is ~ 5-6 per 3 seconds
2 MH Weapon Strikes (DW Fury MH/OH Speed doesn't matter, pure DPS only, so faster usually is better often 1.5ish)
2 OH Weapon Strikes
2 GCD Abilities (Bloodthirst, Whirlwind, or Hamstring usually)

Hunter can be 2-5 per 3 seconds.
1-3 Shots depending on bow speed/haste speed
1-2 GCD Shots (Arcane Shot, Multishot, Steadyshot)

Off my last gruul's lair raid, we had:
Mobile Physical DPS
4 Hunter Pets (2at/3s x4)= 8
3 Rogues (5at/3s x5)= 15
1 Fury Warrior (6at/3s x1) = 6
2 Hunters (3at/3s x2)= 6
1 Prot Tank (Priest Add?) (3at/3s x1) = 3

38 attacks per 3 seconds x8 = +304 / 3s or 101.33 DPS
Not much you say? For comparison on how this actually affects the raid.

A Flask of Relentless Assault is 360 AP, 360 / 14 = ~25.71 Theoretical DPS increase. This still has to go through the mobs physical mitigations, so it is less than an actual 25 DPS increase.

In a non-melee heavy raid, 1 gift of arthas is like flasking 1 to 2 of your melee members with Relentless Assault.

In a melee heavy raid, 1 gift of arthas is like flasking 4+ people with Relentless Assault.

HIGHLY underrated. Use it. End of story.

For those wondering, the rest of the raid was:
Rest of Raid

Non-Melee Shifting DPS
1 Mage
1 Warlock

Other Tanks
2 Prot Tanks (Olm and Maulgar)
2 Hunter Tanks (Kiggler)
1 Mage Tank (Krosh)

Healing
3 Druids
3 Priests
3 Paladins
2 Resto Shamans

Now seems to be counted as a curse. Damn Blizzard for rewarding player's ingenuity and creative usefulness with a big fat nerf.