Looks like the folks at MS have finally released the fix for the annoying Service Pack 2 Expiration Date bug (see below posts).
The installation instructions and links to the downloads of the x86 and x64 fixes can be found here.
You can install this fix either before installing SP2 or after. If you install before SP2 it will prevent the expiration date from being activated. If this fix is installed after SP2 it will remove the invalid expiration date that was set from SP2.
Details on the bug fix is found on the SharePoint blog here.
Enjoy! - M