One of the biggest highlights of PDC 2005 was the first day keynote, when the Office 12 UI was unveiled. I don't know if people realized the significance of what we saw at the time-- but we had just witnessed the death of the main menu.

There's no "dropping down" in Office 12*; it's a context-sensitive tabbed palette interface.

There is no main menu.

That's huge. The main menu has been a cornerstone of the WIMP interface since way back in the days of the Apple Lisa. Julie Larson-Green, the PM of the office UI team, explains:

The main part of the user experience is code-named the "ribbon." It's the one place you go to find the commands that are all about authoring –creating the document, the presentation or the spreadsheet you're working on. There's no longer a stack of task panes and menus and toolbars to look through. There's just one place to look for commands.

UI innovations in Office tend to be rapidly adopted by Microsoft across their entire product line. Not only there, but in third party applications and even other operating systems. Remember the toolbar? That was unknown until it debuted in Word in the early 90's**. Now it's ubiquitous. The "ribbon" is a similar paradigm shift. Eventually we'll all be using these tabbed palettes with nary a drop-down menu in sight. I expect the traditional WIMP main menu to go the way of the dodo soon after the release of Vista and Office 12 in 2006.

* with the apparent exception of the File drop-down, but even that doesn't look like a menu in the traditional sense when you click on it.

** The MS presspass article states that this is "the most dramatic change to the way Office apps work since the introduction of the toolbar in 1997". I think the toolbar goes back much further than that! I just installed a copy of Microsoft Word 1.1a in a fresh Windows 3.1 VM image. Guess what? It has a toolbar. So does Word 2.0.. and Excel 4.0. I don't know what kind of crack those MS presspass guys are smoking..