a Plastic back? I thought they were moving to all aluminum and glass structure on their products. The macbook pro, macbook air, imac, the 3 ipods and the old iphone all have this. But apple took a step back and went to plastic on the 3G? does the plastic back have to do with the new 3G and GPS? They had to make it stick out a bit more so they can throw in the new parts or what?