I think the metallic taste many people pick up is all in their heads. I remember hearing someone from 21st amendment commenting on how the new cans have a water based liner inside the can that negates all of the metallic taste issues.
I'm sure not ALL the breweries use the same cans but still, the pepsi challenge with the same beer from bottles and cans should be done. I bet most don't notice a thing. Surly, Caldera, 21st A..... all of it tastes great to me.