Well, it has finally started for real. I got the Window Phone 8.1, Update 1 upgrade for my Nokia Lumia 822 early yesterday morning (Saturday, 12/20/14).
The upgrade process took a long time, so don't start it until you can be without the use of your phone for about six hours.
I updated two 928s over the weekend. No issues. The whole process took less than an hour. Make sure you are on WiFi before you start the update process