If you are an enterprise administrator responsible for GPOs, I'm sure you've heard of Jeremy Moskowitz and his GPanswers.com site. If you haven't, it's high time you did.
GPanswers has an active forum of knowledgeable people trying to deal with GPO issues. Being the author of the book Group Policy: Management, Troubleshooting, and Security, Jeremy has a lot of knowledge to share. He also offers courses to those who really want to get into it.
Anyway, he just wrote a great introduction to Group Policy Preference Extensions (GPPEs) that you really should check out:
The original Group Policy feature set includes items like Administrative Templates, Software Installation, Security Settings, and Folder Redirection Settings. In all, there are 18 things you can do with the original Group Policy. The Group Policy Preference Extensions feature set adds 21 new features to the existing set, bringing the total number of categories to 39. The goal of the GPPEs is to help you do more with Group Policy and reduce the reliance upon logon scripts. The kinds of things administrators have always wanted to do using Group Policy are now available...