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The Dmg Coefficient has been officially changed to reduce damage on specific DoTs -- Corruption, Curse of Agony and Curse of Doom were all affected. Also, DoTs no longer have a binary resist. This means the game checks for resists on each and every tick.
Some of this info is still a bit off, due to the DoT nerf, however the "Amount of SpDmg Added to Each Spell" section should be correct now.
At Level 70
Spell Hit: 12.6 Rating grants 1% spell hit chance
Spell Critical Strike: 22.1 Rating or 60.6 Intellect grants 1% spell critical strike chance
Spell Haste: 15.8 Rating grants 1% spell haste
Resilience: 39.4 Rating grants 1% less chance of being struck by any type of critical strike, and 2% less damage taken from critical strikes
The following information was taken directly from WoWWiki http://www.wowwiki.com/Formulas:Plus_damage_and_Plus_healing
How Spell Damage Works
Different types of spells have their damage and healing bonuses calculated differently. There are three base types of spells: standard, over time or a combination. Area of Effect and Channeling spells also take different bonuses. After the proper bonus is calculated, penalties are calculated to achieve the final damage.
Amount of SpDmg Added to Each Spell
Corruption: 93%
Curse of Agony: 120%
Curse of Doom: 200%
Dark Pact: 96%
Deathcoil: 80%
Drain life: 71.5%
Drain soul: 215%
Hellfire: 141%
Immolate: 15% + 100% (I think I calculated this wrong)
Lifetap: 80%
Rain of Fire: 76%
Searing Pain: 80%
Shadowbolt: 80%
Siphon Life: 100%
Soulfire: 171%
Unstable Affliction: 120%
Standard Spells (Shadowbolt, Searing Pain)
Standard spells are spells that apply all the damage or healing at one time. To determine the plus Healing or Damage benefit for these spells the following formula is used:
(Cast Time of Spell) / 3.5
3.5+ sec = 100%
3.0 sec = 85.71%
2.5 sec = 71.43%
2.0 sec = 57.14%
1.5- sec = 42.86%
Instant = 42.86%
Over Time Spells (Curse of Agony, Corruption)
Spells with a cast time longer than 3.5 seconds are capped at 100%. The casting time used in the calculation should be the base cast time before effects from talents or gear are applied. Note that the tooltip in game includes those effects
(Duration of Spell / 15) = Total
3 sec = 20%
6 sec = 40%
9 sec = 60%
12 sec = 80%
15 sec = 100%
18 sec = 120%
21 sec = 140%
Prior to patch 2.0.1, there was a 100% cap on over-time spells longer than 15 seconds. This cap has since been removed. The total bonus is divided equally to each tick.
Combination - Standard and Over Time Spells (Immolate)
The bonus for spells that have both a standard and an over time component is divided between them. The over time portion receives the following bonus:
(Duration / 15) / ((Duration / 15) + (Cast Time of Spell / 3.5)) = Portion to Over Time
The standard portion receives the rest:
1 - Portion to Over Time = Portion to Standard
The duration and cast time limits are then applied:
(Cast Time of Spell / 3.5) * Portion to Standard = Total bonus to Standard Portion
(Duration / 15) * Portion to Over Time = Total Bonus to Over Time Portion
Channeled Spells (Drain Soul)
Channeled spells have their benefit distributed evenly over the time the effect lasts, getting 100% benefit for the whole spell (not per tick). The duration of the spell cast time is used as with a standard spell to calculate the total benefit, then divided equally between the number of ticks.
Cast Time of Spell / 3.5 = Benefit
Area of Effect Spells (Hellfire)
Area of Effect spells receive only 1/3 of the total bonus. The cast time is used as with a standard spell to calculate the total benefit, then divided by 3.
(Cast Time of Spell / 3.5) / 3 = Benefit
10 sec = 95.24%
3.5 sec = 33.33%
3.0 sec = 28.57%
2.5 sec = 23.81%
2.0 sec = 19.05%
1.5 sec = 14.29%
Instant = 14.29%
Spells that do Both Damage and Healing (Drain Life)
Some spells, both damage the target and heal the caster. These spells have a 50% penalty to the bonus they receive, but bonuses to spell damage increase both the damage and the healing of the spell equally. These spells receive no bonus from effects that only increase healing.
Rules for Applying +Healing and +Damage
1. Calculate spell time using the base spell cast time before talents and gear. (The in-game tool tip will include those bonuses; refer to WoWWiki's spells section for base cast times for all spells.)
2. Spells that take longer than 3.5 seconds are treated as if their casting time was 3.5 seconds, and spells faster than 1.5 sec are treated as if their casting time was 1.5 seconds.
3. Damage benefits are applied before any talents or buffs that may otherwise increase your spell damage. Healing spells are the opposite: all talents are considered first, and bonuses from gear afterward.
How Spell Crit and Spell Hit Work
Spell crits do +50% spell damage unless you have talents to increase this effect (Ruin). Spell hits do +100% spell damage (since they take away from misses). So in terms of total damage output the +hit with spells will be more efficient until you have reduced your chance to miss that mob to the minimum.
If you have Ruin increases crit damage, then the total added damage is almost the same; +crit and +hit are equivalent in terms of damage added.
Unlike melee, there is a 99% hit cap on spells. Spell casts against a same level mob or player have a 96% hit (no resist) chance, so +hit equipped past 3% in this case is wasted. Level 63 mobs have an 83% hit chance, so +hit equipped past 16% would be wasted. The only limit to crit is 100%, but bear in mind that the spell cast system does not combine hit and crit calculations into a single roll. A spell must hit in order for it to have a chance to crit.
A swing can have exactly one of three outcomes -- crit, hit or miss. The probability for each of these three is calculated separate, the only restriction is that their sum has to be 100%. Let me say again -- Crits can not normally miss. If you are afflicted by debuffs affecting your chance to hit, the amount is first deducted from your chance to hit normally, and then from your chance to Crit.
How Spell Penetration Works
Spell Penetration reduces the resistance of your spell's target. If your target has 50 Shadow/Fire resist, and you have 20 SpPen, your target's resistance is lowered to 30. A target's resistance can no longer be lowered below 0.
How Resilience Works
About 40 Resilience Rating reduces the chance of being struck by any type of critical strike by 1%, and reduces the damage taken from critical strikes by 2%.
