I spotted this on eWeek's Microsoft Watch. For today only, the Friday after Thanksgiving, Microsoft offering a $100 rebate redeemable after purchase of any version of Office 2004, including the cheapest version, "Student and Teacher Edition" of Office. In addition, if you buy any version of Office 2004 (including the aforementioned student/teacher edition) now, you can upgrade to the Office 2008 "Special Media Edition" (which appears to be the primo edition) for just seven dollars. That upgrade offer runs for purchases from back from the first of November to January when version 2008 comes out. But the big $100 rebate is good for Black Friday only.
Slightly more details from Microsoft's Mac blog and Microsoft Watch.