World-of-warcraft – Does Spirit still affect in-combat mana regeneration in Warlords of Draenor

The "five second rule" no longer exists in Cataclysm. You have a fixed rate of mana regeneration while in combat, and another fixed rate of mana regeneration while out of combat.

Out of combat

Your out-of-combat mana regeneration rate is based on your spirit. "Mana per 5 seconds" (MP5) no longer exists on items, and has been replaced by spirit. (You'll still see it on mana oil, though.) Every class that has a mana bar will regenerate mana this way while out of combat.

In combat

All classes start with a baseline regen rate of 5% of your base mana per second. (Base mana is the amount of mana you would have with 0 intellect.) Classes using healing talent specs gain a passive ability called Meditation, which lets half of your out-of-combat regeneration continue while in combat.

For non-healing specs such as mages, warlocks, and shadow priests, spirit does absolutely nothing for your combat regen. Many talents and abilities exist that give you bonus mana in combat, however: Replenishment, Archangel, Hymn of Hope, Shadowfiend, etc. Mages can passively regenerate mana using Mage Armor.

Does this silence suffer from diminishing returns

No. A player who dispels Unstable Affliction will get silenced for four seconds, every time. Here you'll find a list of buffs, debuffs and their diminishing returns updated to 4.3. Notice that the silence debuff you get from Unstable Affliction is nowhere to be found.

What happens when a healer's Mass Dispel dispels multiple UAs? Do those suffer from diminishing returns?

The healer will be affected by a single silence debuff, which does not have any diminishing returns.

How do healers deal with the silence? Can other healers dispel the silence?

There are a few ways in which a healer can deal with Unstable Affliction:

Priests have Inner Focus if they chose the Strength of Soul talent

Paladins have Aura Mastery or Divine Shield

Shamans can use Grounding Totem to catch an Unstable Affliction being casted by the warlock, if they can time it right.

Druid is the only healing class that lacks Silence prevention.

However, any player can use the PVP Medallion in it's various iterations, to remove the silence debuff. Alternatively, humans may use their Every Man For Himself talent to achieve the same result.

This silence effect can be dispeled by another player, too.