It's not democracy, it's just how non-formal language evolves.

People agree on the meaning of symbols/conventions, and then dictionaries draw targets around the arrows.

I agree in principle, but where do schools fit in your picture? Schools should teach you the meaning of things and then, only if the available meanings don't fit your reality, then people should recur to "agreement". I like to think that Shakespeare (or Dante, in my language) words weight more than FB posts to define the meaning of things ;-)

It all depends for whom... Schools are inherently conservative, and slow down the evolution, as did the paper medium for written communications (and iPhone auto-correct).

But now, forget Facebook, think SMS and IM. In 50 years, everyone under 75 will be familiar with its vocabulary, and will have used more for personal communication than the "correct" language. I predict that, school be damned, it will replace the current spelling in everyday life for most people.

Note that I love beautiful language and its historical roots. At the gut level, I find it painful to watch it being torn down. But I'm too young to be a curmudgeon...

I agree with your prediction, but it scares me that a medium that should make communications easier will actually put more barriers between ages.

I already do not understand SMS spelling: in 50 years, probably a 30 years old person will not understand things written by a 15 years old person.

Conservatism in schools has the advantage that we can still read Shakespeare (or Dante) without translation. Languages that change too quickly defy their own purpose (i.e. being a common ground for people to communicate).

I wholeheartedly agree.

Conservatism isn't inherently bad, and innovation for its own sake is idiotic.

Note that, for Shakespeare at least, even though one can still understand the main meaning of the text, a lot of puns and cultural references are lost to the modern reader (lest he's a specialized literature scholar)...

Because that is how languages work. The usage that is most popular becomes the correct usage over time.

But doesn't familiarity supplant or outweigh almost every other facet of UI design?

I think it really boils down to whom you are addressing: people who ignore things are happy to do as others (even if they are wrong -- they don't know!), whereas people who know things care about correctness (and are annoyed by incorrectness or sloppiness).