I've had tons of button issues since my second or third day with it, but only the VOL- button. The PWR and VOL+ buttons work fine. The issue is actually that when any pressure is applied to the back of the phone, it senses that as pressure on the VOL- button. It's easy to work around once you recognize what is happening, but an $850 (I got the 128GB blue) shouldn't need a work-around. It gets annoying when you are on a call holding the phone to your ear or holding it in landscape while playing a game or watching video, or having it in your back pocket while listening to music.
I know there is an update out now that seems to really correct these issues, but it hasn't hit mine yet. Other than that, I love the phone. Pictures and video are fantastic, battery life is ok (not as great as it could be) and the screen is crisp and bright.