I JUST had this happen to me. I've had my phone for a couple of weeks and haven't had this happen before. I regularly run task killer to kill the apps that I don't need to keep running and so I haven't actually had to restart my phone since I bought it. But today, after having sat my phone on the desk for a bit, I picked it up and it wouldn't wake up. I held down the power button and nothing. I thought, maybe the battery was lower than I thought, so I plugged it in and the little charging power light wouldn't come on. Eventually I pulled the battery and put it back in, instant power up this time.
This is the first time, I hope it's the last. This is the second issue I've had with the phone. The first issue I continue to have is my ear speaker doesn't work sometimes after having headphones plugged in. Actually it isn't headphones, but a 3.5 plugged into my car stereo. I pause and then shutdown pandora before I remove the plug, but for some reason, sometimes I have to plug in a headset and unplug it to get the ear speaker to work again.