So many bugs... Apple must have done something drastic here. One theory I read was that Apple was going to add some forward-compatibility with Leopard in their last major release before it - if the last release is indeed 10.4.9, then that could explain some things...
But if there are so many bugs, how did Apple not catch them? Perhaps it was one programmer who simply made a last minute change, or forgot to include a file, and "oops". If it was something so simple, we might see a patch in the next few days.
If it is forward-compatibility, though, there is a possibility that there will be no patches.
For the record, the update went perfectly on my MacBook Pro. Haven't tried it on my iMac, or my family's other iMac, MacBook, or PowerBook. Bit scared to now, actually.