My mother's 822 (black) has had intermittent reboot/shutdown issues since the beginning. My father's (black), my grandmother's (white), and mine (grey) do not. I have discovered ways of triggering the lockups in the past - activating Bluetooth, shutting it off, and letting the phone lock. So far I have not been able to create a lockup on my mom's phone.
I also have been able to create a lockup on mine through Bluetooth as well. Using the same process with the new Bluetooth stack, I have been unable to cause the lockup that I could create 100% of the time on my phone.
From talking with Nokia and Verizon in the past, it is my belief that there's been some problems with the Bluetooth hardware and the stack. It triggers lockups even if BT is not enabled on some devices. There apparently were other triggers as well that made it more common on some devices and less so on others. The CDMA chipset may play a role.
I'll let you know as the days go by since GDR2 and Amber just hit today, but so far the update is promising. Nokia offered to replace the phone at no cost in the past, but they were also honest in not guaranteeing that the replacement would not have the same issues. They told us they were working on it, but at any time they would be willing to send out a new phone. The whole time they were concerned about my mom's needs. It's their first time doing a CDMA smartphone, so it won't be flawless. But their honesty and commitment to making it right was endearing. My mom decided to wait it out because it wasn't so bad as her lockups always occurred when she put the phone in lock mode.
Keep the fingers crossed, but the problem may be solved. And the GDR2 and Amber improvements are also well worthwhile.