While an enhancement shaman cannot provide the same amount of mana return as a shadow priest, the small amount is very good. Grace of air totem is a huge boost to the three casters. ImpDS for spell dmg from the priest and ProM as well as PoH and renew for healing. Fire mage for the single target bosses, with locks bringing all they can to the table. I find that priest > paladin for 5 man heroic and non heroic instances. Full party healing is what a priest does best. I do take a rogue quite often, it is unfortunate they suffer so many of the issues of melee dps.. A shaman is truly better than a rogue for a 5 man IMO. Totems + the ability to back away and heal himself, or use effective range dps if the boss has some sort of aoe dmg ability (whirlwind/earthquake etc) as well as heroism means that enhancement shaman > rogue in my groups. As far as the warrior goes, the more dmg he can mitigate the more dps I can do as a holy priest. I have found that that small additional dps can really speed up an instance.