I don't agree with the Aluminum body. I agree with Samsung's decision to go plastic because it reduces some more weight.
I've the 5.3 inch Notes and its light. Even though the back cover is plastic (its a thin plastic) its not so cheapo plastic. I feel it reduces extra couple of grams more from the device weight.
Plastic makes a portable device much more durable than aluminum. The impact is much smaller when it falls to the ground, because it is light. And the shock is not distributed to the glass screen that much, because plastic is more flexible than aluminum.
I've the 5.3 inch Notes and its light. Even though the back cover is plastic (its a thin plastic) its not so cheapo plastic. I feel it reduces extra couple of grams more from the device weight.