I have installed the huge update with its hundreds of bug fixes, on two Intel iMacs and everything went smoothly. Both machines have been performing well for a couple of days now.
First I ran Disk Utility to repair all permissions, then I did the installation using Software Update. Just to be sure, I ran Disk Utility again, after 10.6.4 was installed.
So far, none of the applications I use have complained about anything.