"In addition to updated anti-piracy capabilities, this update incorporates and improved user installation and validation experience. First there is a new installation wizard (below) that provides more context and information on how the program works. Second the installation wizard offers the configuration of an autoupdate feature so as we release new versions of WGA Notifications that can detect the most current forms of counterfeiting that information can be updated automatically. The wizard also includes immediate results, and improved information for people who's systems don't pass genuine validation."This is an "opt-in" update that will initially be distributed only to systems running four known compromised product keys. According to the announcement, Microsoft plans to update the Windows XP WGA Notifications tool every 90-120 days.
Perhaps a helpful addition is the addition of a new result category which lets users know if the validation result was indeterminate. Resources are provided to troubleshoot the problem, hopefully with contact information for people with legitimate licensed versions of the operating system.
WGA Tool Announcement