I've had ~4 over the course of 2 months. It seems to be related to the stock browser. -Always- while loading an image heavy page after jumping from app to app.
My games (the 300mb to 1gig ones from the play store, like dead trigger and FF dimensions, and my playstation emulator) have never caused a reboot. It seems to be a caching/memory address issue, not processor load.
Under what conditions do these reboots happen? What are you doing at the time? Do you let your battery run low?
To me, when its happened, it feels like a kernel panic and not a hardware (voltage) issue. A few seconds of system lag, then lock, then restart.
Maybe people are avoiding issues by rooting/flashing early?
Well, it's a relief to hear I'm not the only one. This will be my 4th in about two months as well (c'mon FedEx, hurry up...).
The reboots have happened for me under different conditions, but not when I'm playing a game. Often it's been when I'm on Facebook, or switching from one app to another - but several times in the last few days, I've taken my phone out of my pocket to find it in the midst of restarting. Those have been the times that the screen has been frozen and the buttons unresponsive.
My battery is rarely less than about 30 percent.
Your description of "A few seconds of system lag, then lock, then restart" is accurate to my experience as well. It has felt like a memory-related problem... I had read that Jellybean was supposed to be really good at managing RAM to avoid this kind of issue, but that doesn't seem to be the case on this phone.
Maybe I'll look into rooting, etc. to see if it helps. Since I'm unfamiliar with the process, I was waiting until I had more time to learn about it to make sure I did everything correctly, but I may need to make time and give it a shot. I know the resources here are great when I do decide to take that step
Has your fourth phone been as problematic as the other three, btw, or have you finally gotten one that works better?