i did 2 hc´s as a shaman healer yesterday, both dungeons had similar geared groups.
one had a pally tank and a shadow priest dps, so there i had alot of extra healing and replenishment.
the other had a Warrior tank, boomkin and fire mage, i had no replenishment and no extra healing.
the first one went without a hitch, deadmines run through pretty nice with only one dps dying when getting hit by harvest..
the other, Halls of Origin , i was always oom from having to spam heal them, and no, it was not just dps standing in fire and stuff. had possibly 4 wipes there
i finished both dungeons but something as simple as having a shadow priest in a grp can do wonders , i even sometimes try to get a spriest friend to queue with me :P