Minority interest? Yes. Only used by geeks & programmers? Not necessarily...
Ubuntu is a minority interest insofar as it only has a fraction of the users that M$ Windows has. Moreover, despite great improvements in recent years, some configuration issues with Ubuntu are still a pain. However I disagree that you need to be a programmer or a geek in order to use it. And generally speaking, installing Ubuntu on most systems is actually pretty straightforward and generally a lot faster and easier than Windows.
Ironically, in my experience, new computer users with no knowledge of computing at all, tend to take to Ubuntu very quickly indeed. Moreover, Foreign language users in particular seem to like it because the language support is so good.
However some experienced compuer users, the so-called "power users" of Windows systems that often prove to be a much more challenging group. They have lots of applications they are familiar with and moving them to another OS can be highly problematic.
More ironically still, Ubuntu has proven rather bad for one aspect of our business. Our Windows users were always running into problems: viruses, worms, updates that fail, spyware, obscene popups etc. Fixing these issues used to be a "nice little earner".
However we hardly ever hear from our Ubuntu users from one year's end to the next. Our Ubuntu users never had an OS fail to start, or a virus, worm, spy, Trojan, keylogger etc. In fact, in two years of moving people to ubuntu, the only issues we have suffered are hardware failures.
With customer's consent we do monitor and maintain some systems remotely via SSH (secure shell) and occasionally do updates & software installs for them using the same method.
This is handy because we have several users 1500km away in Hungary - users who don't actually speak English. Maintaining their systems remotely with Windows would be impossible - or at least very costly. However doing it with Ubuntu is dead simple and pretty secure, and the tools needed to do it come free with the OS.