I have had this issue, too, where my Droid will just seem to "die" and it won't come back on (even when there's plenty of battery power left.) It has happened three times. The last time it happened, I was on my way to the Verizon store to get help when it magically powered on. I swear this thing is alive!
I don't know if this is related, but I've noticed that sometimes my chargers seem to work with my Droid, and sometimes they don't. It's definitely not the outlets I'm using. Sometimes it seems the charge indicator light will turn on and sometimes it won't. For example, when it won't work in my wall outlet, I will use the car charger and it will go on immediately. And vice versa when it won't turn on in my car, it lights up right away in my house outlet. Anyone else had this problem?