Let's face the real hard facts. Windows users are not educated Computer users.
Linux/Unix are not for the average Joe.
Give a Ubuntu box to any average joe and ask them to use it for one month and then come back and tell you what they think.
It won't be all roses
Well, I consider myself a bit more experienced compared to what's usually understood under "average Joe", but I gave up on Ubuntu as a home OS after a couple of weeks.
You see, to me computer can be either a tool or a toy, but nothing more. Now, as a toy, one can be either playing games or just be interested in tinkering with computers. In the former case there seems to be little alternative to Windows (at least, that's what I hear, not a gamer myself), in the latter - whatever suits your fancy.
On the other hand, if you are actually using your computer as a tool, then you have a purpose - even if it's simply to surf the net. Your goal determines your choice of software and that, the apps you need to use, determines your choice of the OS.
Of course, the "average Joe" typically needs to read emails, surf the web, and type an occational text - simple tasks that can nowadays be handled by any OS. So here things like "ease of use" and "eye candy" come to the forefront and play the decisive role in one's choice of the OS.
On the contrary, any professional would use whatever OS is necessary to run his apps (say, if you need FinalCutPro you run Mac, but OriginPro is only available for Windows, etc.)
My two cents.