This article introduces Group Policy Preferences, explains how they differ from Group Policy settings, compares Preferences to logon scripts, and covers a few Group Policy Preferences gotchas.
The introduction of Group Policy Preferences into Group Policy seems to have quite a few people confused. I think that confusion has been compounded by all of the people who skipped Windows Vista, stayed with Windows XP, and are just now starting to implement Windows 7 on the desktop.
Source : 4sysops