Taking into account the load on Healers keeping up with the damage and mana, when I go Shadow, I back up the group Healer when I see Tank getting low or even the Healer its self and help out when a DPS looks to be imperil.

When the Tank goes to pull, I'll cast Shield and PoM on the Tank then shift into Shadow.
Group Heals looking low on mana? ..I'll pop Hymn of Hope, group low on Health, I'll pop Divine Hymn.

This perhaps is an alternative grouping method (Backup Heals)

Edit: Perhaps on some Bosses, 2 full Healers ?
Edited by Kilee on 12/14/2010 9:26 AM PST