I think there's a quiet majority out there who's never tried anything but Windows, and think of their computer as nothing more than a tool, completely oblivious to such abstractions as operating systems.
I don't see many problems with Windows apart from it doesn't like moving User documents/data to another drive. The resulting clutter from that is all down to me though. I haven't had an complaints with Vista.
I'm warming more to Ubuntu now (although I only use it as a development platform on a laptop, I'd probably prefer it even more on the desktop) but I really don't see the "horrors" in Windows.
That was pretty much what sold me, I was 30 something hours into a Solidworks project that forced me to use Windows, and the machine BSOD me at 4am the day it was due. If you rely on a machine you have to have faith it will work during crunch time.
I feel more comfortable in Mac OS, though. I've used Ubuntu a few years back and prefer that over Windows as well.
Some people just resist any kind of change - they're used to Windows, they aren't going to try anything else, because they think (and they might be right in theory) that they don't need anything else.
I think most seniors can just about already switch fine to Ubuntu.
Applets - they don't suck as badly anymore!
There is an alternative, but it's not all sunshine and green grass either side.
/opt and /usr/local are generally unpackaged guff.
I use Linux/Mac/Windows every day and have no trouble switching between them. If you are suffering under either Mac or Windows, it's your fault, not the OS's fault. If you're suffering under Linux, it's because you aren't enough of a moron to be a full time computer geek like me.