QUOTE(Rich Smith @ July 3 2008, 07:57 PM)

First time I've heard of the Combo Update. What's the difference?
The combo updates tend to be a lot more reliable than the OS updates through Software Update utility. My understanding is that they completely remove certain files and replace them, instead of overwriting them, which apparently is what Software Update does.
As Hugh said, they also span many updates, so for example if you were running 10.5.1 you could update to 10.5.4 without running the two updates in between.
Combo updates are much larger files (This one came in at a whopping 544 megabytes or something - in comparison, Software Update's version was 59 megabytes) which further makes me believe that they do literally replace the patched files with completely new ones instead of overwriting.
Good times.
Enjoy!