Well, as with any .0 release, it's always going to have issues, hence why 10.3.9 was very solid for Mobius Rex. Of course, that upgrade didn't go smothly for anyone either.
As for usage in 10.4.3, I'm actually quite happy with it. It works like a champ and has yet to crap out on me. Only once did I get a kernel panic but that was of my own doing.
My only issues with it are the interface inconsistencies. If they could just fix that up, I would be happy. Considering that KDE does a good job of trying to unify different widgets like GTK and others (sometimes through the help of the gtk-qt engine), and it is by far
nowhere near the ease of use of OS X, why is it so hard for Apple to do the same if not better?