Gartner analysts said at a Gartner-sponsored conference in Las Vegas that Microsoft Windows would collapse.

That Microsoft has an increasing problem with Windows can be seen without the Gartner analyst hat on. Linux on the desktop is ramping up via low-cost hardware and Apple continues to steadily gain market share. Windows Vista adoption is slow as Windows users would rather stick with XP.
The Gartner analysts cite as one of Microsoft’s problems the rapidly-expanding code. That is why they ran into delays with Vista.
Windows got too fat and the new trends are slimmed down task focused OSes and of course online Apps. Microsoft is like most of the time behind the curve.

On the other hand the install base of Windows is still gigantic. Microsoft has a lot of time to fix everything that is needed in Windows 7.
More details on Computer World.