My first Galaxy SIII was very very fucked.
Camera had a dead spot on the CCD in the bottom right hand corner, giving every photo + video a black splodge.
That plus Orange (UK) broke something in the firmware when they branded it, yeah not the nicest thing to see when you bring your brand new phone home, an ugly Orange logo splash screen on the phone. Then finding out the phone would laaaaag whenever hitting home button. I'm talking a full 2-3 seconds before the widgets and menu bar would load. Wi-Fi would also drop out every time the phone when to sleep, would only reconnect when you turn it off and on again. Audio was also broken, would glitch every 10 seconds during calls, giving a digital squeak.
Took it back to Orange and got it replaced 2 days later. Immediately flashed it with stock unbranded ROM. Had it for a week now and it's fixed everything.
Moral of the story, if you got a branded phone, unbrand it. Plus check your camera for dead spots. I have found zero other results of this online, however you never know.
Phone is nice though, makes my old Galaxy S1 feel like a brick and my iPod Classic look like a cartoon bulbous toy. Still a slight bit of lag in returning to home-screen, however it's less than a second. I imagine this will be eradicated with Jelly Bean (god praying it comes soon).