I believe that the key reason Unix hasn't taken over the generic office desktop has nothing to do with the technology and everything to do with the people and processes involved.
Thus the generic corporate PC user I talked about yesterday would be completely unaffected if someone snuck in overnight and replaced the PC running Windows/XP below her desk with one running something like Ubantu Linux - as long as our saintly break in artist perpetuated her login ID and password while ensuring that whatever application client she uses first, auto-starts on login.
And that reality raises a question: since, in theory at least, this would save larger organizations some serious money, why don't we see it happening everywhere?
And the answer, I think, is that the IT groups in place in most larger organizations are now numerically dominated by people whose roles and self imagery depend on knowing something about using the Windows PC - and asking them to implement desktop Linux is like asking the Marlboro man to see himself as a victim still clutching his parasitic badge of poverty as they wheel him off to the cancer ward. It just isn't going to happen - and if upper management insists on trying to force it, well then the wheels are going to fall off that chair and everything else will go expensively wrong until management folds its tents and retreats into the shared Shenandoah valley dream.
The bottom line is a simple, and unbeatable, consequence of human nature: if you don't align your technology with the values of those charged with making it work, they won't.