Mine was a little different. I was on a road trip and the maps app was having a hard time finding me (fortunately I knew the route well enough that it wasn't a major concern). I first closed all my idle apps, and the phone froze for just a few seconds. I decided I needed to restart my phone, so I held the power button and nothing happened. I tried it again three or four more times and the screen went blank. Nothing I tried could get it to do anything. I knew it had just over 50% battery, so charge wasn't a concern; but I tried plugging it in anyway and it vibrated just like it normally would. I then went to bed with it charging.
This morning I played with it again, I noticed that the mute switch also made it vibrate, but nothing else did anything. I even plugged it into iTunes, but my computer came back with an error.
I looked on this forum and found the idea to hold both the power button and the middle button, that worked. I'm happy to have my phone back, but I'm not really convinced that this will never happen again...with 7 pages of posts I hope apple takes a serious look at the problem.