I have healed a few instances (Nothing higher than SM Cath)
I'm 10 pts Holy
Rest in Ret.
I find that putting up Defense has been generally pretty good. I have used Shadow Resist and Fire Resist, but it was very situational. I ran once with 3 casters - Me Paly Heals, 2 mages, Druid tank, and a hunter. I tried the anti-spell interupt aura, but it wasn't worth it.
I bless DPS Melee with Might
I bless Casters with Wisdom
If DPS misbehave and pull agro - they get Salvation (Reduce Threat)
To be honest when I play as my mage - I prefer BoK and BoW about equally. Kings helps in many ways, but honestly - Most runs are about speed. The few extra DPS I get from Kings are nice, but, without testing this hypothesis - I think the added +Mana Regen is my preference. (aka - less time drinking water is more time pew-pew) Both seem pretty good. I haven't run any Heroics, so maybe BoS is the way to go there. No idea personally.
*That being said - most Paly just drop BoK on the mages.