Mac update software vs "clean install"
Found this on another web site -Mac can be slow after a software update because of the number of files changed.
In activity monitor - there is a job called fsevend - and it feeds off a hidden file of same - and generates applications listed by changed files.
On a clean install (delete the drive) you have to set all you defaults - so you can prevent the system from going on-line until you are ready. On an update - apple resets defaults to automatically connect - and probably push more downloads - so if you try to do any work - the fsevend gets overwhelmed.
Bad show on apples part that they do not step users through a software update (or do it for them)
Mac OS X (10.6.8)