The big player here is unquestionably Microsoft. Their latest OS is WindowsXP. Nothing needs to be said here. The OS is centered around the desktop metaphor and despite some artistic changes after Windows 2000, computer-user interaction is essentially unchanged since windows 95. Their next OS is around the corner but we can't really draw any solid conclusions since most information is preliminary. Testing builds and screenshots can never say anything for the finished product.
Leaving aside the under-the-hood changes (such as the search based filesystem if and when is included) the screenshots really don't show any radical changes. It is clear that Microsoft has thought that many users will want to view pictures and manage a large music collection with their computers so there are specials filter facilities (also known as virtual folders) for these, but other than that, things stay the same. The much-hyped sidebar (which appears and reappears between builds) is also another interesting concept but all demonstrations of it, copy functionality from existing third-party applications for Windows XP.
The "My computer" icons was not present in Windows XP (leaving only the recycle bin on the desktop), but we are not so sure what will happen with Vista. After all, many users will just re-enable it every time they do a clean install of Windows XP. The Vista interface looks more polished than previous versions and there is certainly an effort to reduce interface clutter (Gnome development heads this way too, KDE is not but simple KDE has recently appeared).
The other visible changes such as the transparent window borders or the 3D task switcher may look cool but really add nothing to usability. The former already exists for some years in complete Desktop Environments like KDE and even in lightweight Windowmanagers for Unix like fluxbox. The latter exists since 2001 in Sun's looking glass. If these ideas added anything important to usability they would have become widespread by now. The Expose feature introduced by Apple (and copied by many DEs/applications/plugins) is one of the best ways to locate a specific window under the pile. We would prefer better a new "live" desktop instead (not based on the Active Desktop Idea which has failed), but this doesn't seem to be the case with Windows Vista.
Nobody can accuse Microsoft for what they do. They have a vast user base so they can't just change everything overnight. But one would expect that after 5 year of development the new OS would attempt some change in workflow. Especially since Microsoft targets other areas too. Windows Media Center boxes have no place in an office environment so there is no reason why Microsoft could not propose a different approach for their desktop OS too based on "consumer device" ideas.
The next big player is Apple. Apple is considered the major innovator in computer usability. They were the first supporters of the desktop metaphor at the same time. The recycle bin is their invention. It is one of the few companies that doesn't fear major changes. The change from MacOs classic to Mac OS X was certainly a big one. It has not however changed the main concept. The recycle bin is still there, the finder/file manager, the applications and documents etc.
We don't think that Apple will leave the desktop metaphor at least in the near future. The first reason is that the Apple desktop is mature, well integrated and certainly well thought. The flaws of the desktop metaphor are hidden behind brilliant Apple Engineering. The Apple desktop is considered the best of its kind and several other "virtual desktop on your screen" environments, still copy its ideas. The second reason is that the Apple desktop is the base for several vertical market applications (image, video, audio/editing/desktop publishing etc.) which brings us to users who are interested more in the application than the desktop environment, as already discussed.
Apple has also its own implementation of a "live" desktop. It is called dashboard and is quite interesting. The dashboard allows the user to fill the desktop with little elements (called widgets) that show useful information at any time. The list of widgets is extensive. Nothing really groundbreaking but still a great idea and an even better implementation.
Apple is still a great company. They have been in the headlines lately because of the switch to x86 from PowerPC. This has nothing to do with usability but it shows that a great company does not fear to break free from old concepts (Apple=PowerPC) and do what is best for its clients. When Apple engineers are fed up with iPod sales and start to think the next perfect user interface nothing will stop them from implementing it.