Sometimes it can be difficult to explain in just a few short sentences how permissions are defined in SharePoint 2007. Especially since so much has changed since 2003 / v2. Shane and I covered a fair bit of the detail on this stuff in our book Beginning SharePoint 2007 however I just (re)discovered a fantastic article by Joel Oleson from last year that I will be referencing when trying to explain to people as well. I highly recommend anyone that is responsible for managing their SharePoint environment (whether MOSS 2007 or WSS 3.0) to grab a coffee and sit down and review this line by line.
Just posted on the SharePoint Team blog is a bunch of information and links to the newly released Infrastructure Updates for MOSS, WSS and Project Professional.
These updates include bug fixes, performance enhancements as well as new functionality and features around Search. According to the blog post, it is recommended that all customers install these updates to take advantage of the improvements immediately.
I will be doing some updates over the next few days on my own machines as well I am sure we will be patching our many development environments at work. I will post any personal findings and experiences as they become available.