Blizzard has limited a groups ability to progress by limiting the Mana Regeneration of the healers.  If a group has weak tanks or slow dps, the healers will run out of mana.  I say this because I want to address Spirit.  When I refer to Mana Regen, I mean "during Combat".  Shamans talent themselves into Mana Regen through Spirit.  As we reforge to obtain our minimum Haste, we must be careful not to do it at the expense of Spirit.  Think of Haste as an "Anti-Spirit", the more Haste we have, the more Spirit (Mana Regen) we need.  Reforging more than a 100 or so Spirit to meet our Haste gains should be avoided, unless we find ourselves with no Mana Regen problems and can afford it.  Once again, I avoid reforging Spirit to meet my Haste requirement and reforge Mastery to Haste instead.  All healers run out of Mana ... it is a fact.  We need enough Spirit to keep our Mana Regen during combat above 2400.  If you are easily maintaining your Mana at that Regen rate, you need to find a group doing more difficult content, or you aren't pumping out the healing you should.  I use Trinkets as tools to supplement Mana Regen.  Haste therefore is a "two-edged sword", and though it is as viable as Crit and Mastery, it creates a Mana Regen burden.  Crit is always there, but uncontrollable.  Mastery is sometimes there and excellent when needed.  So I gem for Intellect, Crit (Yellow) and Spirit (Blue).  I reforge out of Mastery to gain the Haste minimum.  Once I reach the point where I no longer have to reforge Mastery to Haste, I will then reforge Haste above the minimum to Crit  (now if I only had the gear to do that ... hehe).