First stop would be to check out the recently published TechNet Article Recommended Updates for Group Policy in Windows Client and Server Products

Then take a look at this list of recent  old Group Policy Hotfixes released from Microsoft.

Note: This page is no longer updated. Please follow me on twitter if you want notification of new Group Policy related hotfixes.

If you want to keep track of all new Group Policy (and Active Directory) hotfixes yourself then check out the Microsoft AD team blog at  Ask the Directory Services Team