Not much to say about this one. With Microsoft Office 2008 Service Pack 2, a bug was introduced that prevented all the Office applications from opening some of Microsoft's Open XML documents, templates, and macro-enabled documents and templates (see "Microsoft Releases Office 2008 Service Pack 2," 2009-07-20). Several commenters on our article about Service Pack 2 had the problem, though all the .docx and .xlsx documents on my Mac seemed to open fine.
Microsoft has now released the Microsoft Office 2008 for Mac 12.2.1 Update to fix this problem. In my initial testing, it was still able to open the Open XML documents - if you weren't seeing any problems before, it's probably not essential that you upgrade immediately. The update is a 23.8 MB download, and is available from Microsoft's Web site or by choosing Check for Updates from the Help menu of any Office 2008 application.