MS recently posted here that SP2 has a bug that incorrectly activates the Product Expiration Date within MOSS.  Basically this means that 180 days after applying SP2 SharePoint will expire, as if it was a Trial Installation.  They're working on a resolution to this fix and hope to have it out PDQ.

They've posted a manual workaround here but this link appears to be "broken" for now, but should be up within 48 hours.

Note the affected products: SharePoint Server 2007, Project Server 2007, Form Server 2007, Search Server 2008 and Search Server 2008 Express.

Stay tuned as more info comes out...

- M