Windows 7 and Windows 2008 R2 are having real good amount of new GPO settings that IT administrators can manage on their Client and server computers. These includes, controlling the USB devices, configuring firewall rules, and many more. One can go through gpedit to get a understanding of all the settings but that is time consuming.
I came across these nice downloads from Microsoft which describes significance of each settings, their options, and the corresponding registry keys if any. Using this sheet you can quickly search for a policy and understand its functionality.
Download these reference guides from MS download center