Even Gartner, who I have always thought as company that has over-hyped Microsoft, has come to realize that Vista was a horrible horrible mistake.
The entire Windows eco-system is collapsing because it is too big and not secure enough. So much of the corporate expense of Windows is not just the Microsoft licenses, but the huge cost of management and security software. This cost also includes massive hardware costs that are incured by every system that needs to run that software.
I think the tipping point is here. Look at the success of hardware like the Asus Eee laptop. Apple! Are you listening? Blot is out and you are next on the chopping block if you aren't careful!
I was just messing around with my Zaurus PDA this week. I've been installing Android, the gPhone software. I also installed a full debian distro on it called Titchy Linux. Then I installed Angstrom, which is also a Linux distro based on the former OpenZaurus project.