I have tested running AE CS5 10.0.1 on Mac OS 10.6.4. Very time i render something i takes longer than on a AE CS5 10.0.0 on Mac OS 10.6.3.
Rendering the same stuff took me nearly 2 hours more on the version that does not have the latest update.
My current preferences is set
Installed RAM 8GB
RAM reserved for other 2GB
Installed CPUs (processor cores) 8
CPU reserved for others 2
RAM allocation 1GB
Retrieving data ...