I got the update message last night, and silly me didn't check here first, just chose "Restart" or whatever the option was.
Install looked to be going ok but then got stuck in the gear cycle, and this morning it was still rebooting every minute or so. Phone was plugged in but there was no red charging light.
Could not power off the phone completely, no matter how long I tried holding down Power.
Was able to get to the barcode screen, but even power down by holding the camera button would trigger a reboot.
Eventually figured out how to get to the Lightning bolt/Gear combo screen (VOL+ on reboot) but that didn't help.
Installed the Windows Phone Recovery Tool but that didn't help - when I did a manual detect, it found the phone but there is no software on the server for it to find and install.
I went to WindowsPhone.com and tried to Ring My Phone but it can't be found right now, so I'm guessing it also won't be able to do a remote factory reset. To be honest I don't want to try as I don't really want to wipe my phone.
Guessing that my battery level was not sufficient to complete the install, I tried draining the battery because as I said before it would not charge. Found that holding VOL- made it reboot vibrate reboot loop, so I put a rubber band around the phone and let the battery drain. Eventually the screen turned off, phone was dead! Yay!
Plugged it back in and got the red charge light on finally(!) and got the battery icon on the screen, but after a few minutes the phone rebooted and went into the original gears loop.
After 30 minutes or so I put the phone back into Lightning Bolt mode. Red light shows it's charging, so that's progress over earlier this morning.
If it doesn't work after it's fully charged then..... ????