I have a Sony Xperia Z which I was very happy with until recently.
First, an Firmware update destroyed the battery runtime, then another one fixed this, but the phone was laggy as hell THEN the lens permanently fogged up from the inside with dust (this phone is waterproof, how did that happen??).
I was close to buy the new MotoX, but decided to follow the Self-Repair Manifesto and 'own' this phone. First I installed Cyanogen Mod to make it fast and stable again, then I fixed the lens fogging. I had concerns about that as everything is glued together but it was really easy. You only need a hot air gun and a suction cup.
Anyway, I tried how easy it is to remove the black coating of the back glass... you see the result below. =)
The mainboard was covered by the NFC antenna, so I moved that over the battery.