One thing you might want to note - it took a very, very long time to re-boot after the update. I don't know if others had the same experience, but I was getting quite concerned before my machine finally showed me the login screen.
For myself (I made the original comment) it was the first time only. Nick mentions this also happened with previous OS updates. True here as well, but the 10.4.5 update seemed to take much longer than the previous updates for me.