Hotfix for SP2 issue that reverts SharePoint products to Trial Version has been released
Microsoft has released a fix for the SP2 problem that reverts the license into a Trial version after installing Service Pack 2.
More details can be found in the following KB article:
971620 - When you install the 2007 Microsoft Office servers Service Pack 2, the product expiration date is activated incorrectly
For your convenience here are the download links for the fix:
[Update June 26th] Additional info from SharePoint Team blog: We will be updating the existing Service Pack 2 download package with a new package that includes this fix within the next 4-6 weeks.