Mail specialization
Starting in 4.0.1, shaman will receive a 5% bonus for wearing all mail pieces (except for the obvious slots which are type-neutral, like rings, cloak, trinkets, neck, offhand, and relics). For most shaman, except maybe those leveling, this 5% bonus to intellect is enough to outweigh the benefits from any leather/cloth upgrade that you currently are wearing, because as stated above, 5% Intellect not only increases your mana pool (which accordingly increases the amount of replenishment you gain), but it also increases your spellpower, your crit, and scales with gear, making it that much more powerful the more equipped you are. Just a note: on patch day, you will need to visit your trainer to learn mail specialization; you will not pick it up automatically.
Ditch the Cloth/Leather Pieces , really?
I’m sorry to say, but the Plague Scientist’s Boots, Phaseshifter’s Bracers, Leggings of Woven Death, and any other cloth/leather items which might now be supplementing your gearset will need to be swapped out with the mail equivalent for you to benefit from the Mail Specialization passive talent. So, the 16 Int, 0.5% crit, 7 haste, and 26 spellpower that I’ll be losing swapping back into Earthsoul Boots and Bloodsunder’s Bracers will be mitigated by the 91 Int (plus 98 sp, 1365 mana, 0.05% crit) I’ll be gaining through Mail Specialization.