I had my iPhone 5 for a week and one of the volume buttons failed (stuck / broken). They replaced it no problem at the Store; HOWEVER the replacement unit has this very loose power/sleep button issue. I took it back to discuss this and to ask for a replacement, but they refused stating that it's still functional and that some iPhones "are just like that way".
I absolutely love my iPhone, but the first button issue and now this extremely annoying second-rate replacement issue has left a very sour taste in my mouth. I'm quite surprised to be honest, because I've had such great support from Apple in the past.