Windows 7: The $1930 Upgrade
pcworld.com
pcworld.com
The problem that Microsoft has gotten itself into is that Windows XP is "good enough" for most things, especially in the corporate setting. There just isn't enough "new" to require moving an entire organization to Windows 7 when XP works just fine. The other problem is that computers have gotten to the point where a low-end model is also good enough for most things. A 3-5 year old desktop is still a good machine for most office work. So why would an org buy newer machines to replace ones that work just to run a new version of Windows?
When you talk about moving to Mac OS X or Linux, the scenario above falls apart. Since you're talking about making a major platform shift, there must be a good reason. Perhaps it's support costs. Perhaps it's productivity (perceived or otherwise). Perhaps it's to get the most out of the hardware you already own with minimal software costs.
Once you start to entertain the idea of migrating away from Windows apathy isn't an issue.