Actually, from what I hear, you need 3 Shaman in a raid group for later raids:
2 Resto, 1 Enhancement.
Windfury in a melee group (usually 2 or 3 rogues and a fury warrior) is -huge-, or stick the Enh Sham in the tank group for the Windfury on the tank for extra threat. There's a bit of versatility with an Enhancement Shaman in a raid, although you don't want to stack too many of them.