OS X users, 10.4.9 update
I just thought I would re-iterate to everyone using OS X that you take care when updating to 10.4.9.
It is a finicky update and if not run correctly, will keep your machine from booting. Do a backup (Carbon Copy Cloner to a Firewire drive is what I suggest), close all applications, and install.
I found that downloading the combo-installer if on an Intel machine is your best bet (instead of the Software Update).
Just a heads up.