I recently bought a stainless steel replacement back for my iPhone 4, and just got around to installing it today. There’s nothing wrong with my original glass back, I just like the look of the stainless steel. It was really simple actually, I bought a “000” Philip’s head screwdriver from my local hardware store and followed the instructions on iFixIt. My only complaint is that the anchors on the new back panel are plastic, unlike anchors on the glass back panel from Apple, which are metal. I think I may have overtightened one of the screws and stripped it a little (the plastic anchor, not the screw), but it seems fine.