If heroics is your overall goal... it is POSSIBLE to do a lot of the content with 5x shamans, but not all. There are a handful of encounters that simply need a real tank. That being said, 1 pally + 4 shamans is still good if you want to PVP... just drop the pally and go in with 4

My primary goal is PVP with a limited amount of Heroic badge farming... so 5x shamans is good for me.