The SharePoint Team blog announced a major bug with SharePoint MOSS SP2:

This is funny, but extremely serious and important.

During the installation of SP2, a product expiration date is improperly activated. This means SharePoint will expire as though it was a trial installation 180 days after SP2 is deployed. The activation of the expiration date will not affect the normal function of SharePoint up until the expiration date passes. Furthermore, product expiration 180 days after SP2 installation will not affect customer’s data, configuration or application code but will render SharePoint inaccessible for end-users.

http://blogs.msdn.com/sharepoint/archive/2009/05/21/attention-important-information-on-service-pack-2.aspx

• Does not affect data
• But it will silently deactivate after 180 days
• Users can come to work without warning and SharePoint will be unavailable.
• If you are installing SP2 - apply hot-fix from MSDN immediately afterwards.
  • Download here http://support.microsoft.com/kb/971620
  • You will need your product-ID

Get the word out.