A particular issue was the possibility of remote code execution triggered by maliciously crafted RTF emails.
Patches were immediately available for Office XP, 2003, 2007, 2010 and 2011, but a footnote to the list of affected software stated "The security updates for Microsoft Office 2004 for Mac, Microsoft Office 2008 for Mac, and Open XML File Format Converter for Mac are unavailable at this time."
A month later, the situation has improved slightly.
The Office 2008 12.2.8 update fixes the RTF email issue along with other vulnerabilities, and also delivers a fix for an Entourage bug that could cause the program to quit when opening an email containing inline attachments, sending an email, or clicking meeting invitations.
As of this writing, the corresponding updates for Office 2004 and Open XML File Format Converter had not appeared on Microsoft's web site.