Today Microsoft has released the final version of Service Pack 1 for Windows 7 and Windows Server 2008 R2 for general public. The build no. is 7601.17514.101119-1850
Windows 7 Service Pack 1 (SP1) is an important update that includes previously released security, performance, and stability updates for Windows 7. SP1 also includes new improvements to features and services in Windows 7, such as improved reliability when connecting to HDMI audio devices, printing using the XPS Viewer, and restoring previous folders in Windows Explorer after restarting. But the impact of SP1 on the Windows 7 client operating system is considered to be minimal but for Windows Server 2008 R2, it has a number of powerful virtualization features i.e. Dynamic Memory and Microsoft RemoteFX.
In order to install the Service Pack 1 of Windows 7 and Windows Server 2008 R2, your PC must be running RTM version of Windows 7 or Windows Server 2008 R2. If you installed a pre-release build (beta or RC or whatever leaked build), you will need to uninstall it before you can install the final release of SP1.