And I hate, hate, hate it.
I think the worst case was Harry Turtledove's Case of the Toxic Spelldump, where the main character purports to be a Jew. Goes to the synagogue, even. He's an idolater. He explicitly thinks that his belief (lumped in with others) creates that which he worships. Silly, silly, silly.
But it's seldom better in explicitly polytheistic systems. It seldom allows the Powers That Be to be noticeably numinous. And, oddly enough, it tends toward the gods acting like three-year-olds. Despite the obvious problem of -- if the humans made them like this, why oh why are the humans any better?