Today, Microsoft released Service Pack 2 for Windows Server 2008 and Windows Vista.
Service Pack 2 (SP2) for Windows Server 2008 and Windows Vista is an update to Windows Vista and Windows Server 2008. It provides customer and partner feedback-driven fixes into a single service pack, minimizing deployment and testing complexity. In addition to all previously released updates since SP1, SP2 supports new types of hardware, and adds support for several emerging standards.
Details and download links can be found at http://technet.microsoft.com/en-us/windows/dd767623.aspx?ITPID=wtcfeed.
Notable changes in Windows Server 2008 SP2 and Windows Vista SP2 can be viewed from this link.
Along with all the other fixes and rollups that are currently available through hotfixes and rollups, it includes improved power management and new Group Policy settings.