Same thing happened to me. Got the popup, rebooted but it didn't go to the unpacking screen, just right back to the launcher. Was still on 2.2.1 and "checkin" didn't find any updates, and system said there were no updates to install. No more popups, either, that there was a 2.2.2 waiting.
Turned it off, yanked out the battery for 30 seconds, put it back in and turned it on... got the popup pretty quickly and tried the install again, this time it worked and I'm on 2.2.2.
same for me!
1. first notification simply reboots
2. powered off, battery pulled off
3. powered on, second notification immediately... 2.2.2!
as we know, root has gone but... how it happened?
su, busybox and Superuser.apk are still in their places with 755 permissions, it seems it's not necessary to do all the rageagainstthecage steps again... where's the deal?