What would you prefer then?
Plastic? Maybe something that's more soft to the touch, grippy. I don't mind the glass...but I hate the current 2 completely flat surfaces, and I doubt they would make the back similar to the iPad/iPod/iP3g/s with glass, so that's out of the question.
As far as aluminum, that doesn't exactly inspire confidence in holding on to it. Are the current iPod touch's backs aluminum? Because they aren't scratch resistant at all from what I've seen...and would dent easier I would think as well.
Or, you know, wood. lol Never have seen that before, pretty funny.