Jeff Atwood points out that the big news from the recent Microsoft PDC demo of Office 12 is the death of the main menu. Instead of a traditional main menu, Office 12 will have a series of tool palettes selected by tabs where the main menu used to be. I think he's right, that we're in for another big shift in UI paradigms, as Office leads the way for developers everywhere. It may be difficult for me-too developers to adjust to this large a change, though, so I don't think the main menu is really dead.
For me, the screen shot of Office 12 prompted a different thought: "Isn't that a Mac?" Could they have copied more of the look of the Mac UI??