I, too, bit the bullet and did the upgrade on the way home from work this afternoon. Worked great, exactly 20 minutes and it was done. I waited until I got home to turn the car off and back on.
I didn't wait after turning it off, and that may have caused a slight problem. Navigation went on for about 15 minutes without rebooting and downloading contacts also wouldn't complete.
I then turned the car off, opened the door and shut it, then waiting about 5 minutes. When I restarted the car, the map came right up. Downloading contacts took just seconds.
The biggest pain was getting the file to unzip properly. I couldn't separate the two files needing to be in the root directory from the zip file. I finally got it to work, and everything else went well.
Thanks to all who came before me and educated us on this process.