Contributed By: Cliff Hobbs [MVP SMS]
Reproduced from the Microsoft Software Update Services: Frequently Asked Questions web page:

http://www.microsoft.com/windowsserversystem/sus/susfaq.mspx#top

"The Automatic Updates user interface (UI) is probably not hanging but is instead waiting for the service pack install to complete. There is no animation to indicate that the install is continuing, and you will not receive feedback about the progress of the install until it is complete. This is especially true since the service pack install is done in quiet mode with no UI from the service pack installer. The service pack install can take several minutes, especially on slower hardware, so the best option is to wait until the Automatic Updates UI indicates that the install has finished."