It takes guts to do it right.

One thing I've come to realise recently is this: Stamina is good for all classes.

Whilst there's an overwhelming urge for classes to focus on their "active" stats, be they Intellect, Healing, Damage, AP, MP5, etc, there's one universal truth in raids and heroics: sooner or later you will get hit.

Wether it's an AoE, a random targetted ability like a charge or some other trick, most encounters are designed so that the tank can absorb most, but not all of the damage an encounter puts out. If Blizz didn't do this, then all healers would have to do is target the tank, spam their heal buttons and victory would be assured.

In Raids and Heroics, the mobs hit hard, and a cloth-wearer with 5-6k health can easily be one or two-shotted. If that's a damage-dealer it's annoying. If that's your only healer, then chances are a wipe will ensue. Swapping some DPS/Healing gear for some with more stamina can turn a loss into a win. Ideally, a ranged character should have at least 6.5-7k health unbuffed, and a melee character should have between 7-8 to survive in Karazhan or Heroics. Beyond that point I'm not sure, but you can't go wrong with survivability.