I did a "Clean Install" - I wiped my PowerBook and installed onto an empty drive.
My reward was the exact same Blue Screen followed by the spinning Beachball - it had me quite nervous for a number of minutes.
In comparison I "updated" my G4-DP without a hitch!
The only thing that was irritating is that the updataed machine also updated Mail.app with all of my mail-accounts. After a "Clean Install" Mail.app wil import all of the old mails from a backup but refuses to recognise mail-accounts...
... does that make sense?
Looking Forward to 10.4.1