The update completely screwed up my sorting. Some artist names were changed to "unknown", some were changed to other names, and lots of other weirdness abounds. My library is now a complete mess. Wait until 10.0.1.
STAY AWAY FROM THIS UPDATE, SEE ABOVE
let me think now.
I'm going to upgrade.
So - back-up, perform upgrade. Any problems - revert to back-up.
No issues here, not seeing any other users with issues. Sorry for yours, but it sounds like a database corruption of some sort. Did you have lots of (ahem) 'downloaded' content kicking around? Revert to your back-up, try again later.