Phone gets all sluggish and the lower rear of the phone gets really warm (nearly hot) to touch.
Sometime it'll get sluggish and I experience problems, last two were:
1) Can't open Settings, power cycle the phone to fix
2) Voice search in Maps crashed back to Home screen, power cycle the phone to fix
Both happened today, less than an hour apart, and both times the lower rear of the phone got really warm.
Another issue was rearranging apps on the pages, and it would "vanish". It's not on another page or folder, and I was no where near the Trash/lower part of the screen.