Existing users, 
The reason why this requires a restart is because it does something that can't be installed via drag-and-drop - it installs a new version of the Foundation library, which is used by every Cocoa application, including loginwindow. So the only safe ways to install the update are to either:
(1) reboot
(2) kill and restart the window manager (which means logging in as ">console")
#1 is much easier to do than #2, which is why Software Update does it...
Oh, did I mention I had no problems with this update? Kudos to Apple for releasing it.
Apple Security Update
for PPC OS X 10.4.11
Version: 2008-008
5 stars to offset DodgeNeonRT's review
Feedback Type: Review
Contributed by: nickzman Friday, December 05 2003 @ 05:52 PM PST
Product Platform: MacOSX
Used Product For: Have Not Tried
Recommend Product: YES
Overall Rating:
Quality / Stability:
Comments
5 stars to offset DodgeNeonRT's review - Lou Zer
If you want to know everything that is installed, then download the update, but don't install it. Rather, open it up using Pacifist and read the BOM file.Saturday, December 06 2003 @ 03:51 PM PST
5 stars to offset DodgeNeonRT's review - Eupfhoria
Which would cause everyone to know about security wholes in unupdated macs.Friday, December 05 2003 @ 10:08 PM PST
5 stars to offset DodgeNeonRT's review - brossow
Well, then -- you know what? Maybe Apple should say that instead of saying that it updates Safari, which according to you it does not. I'm tired of Apple being only slightly more revealing in what their updates do than the LimeWire people. I want to know exactly what is being installed and where; it's my computer and I think I have a right to know what the update is putting on my machine.Reply to This
Friday, December 05 2003 @ 07:57 PM PST