They had a brief vignet on dictionaries on the radio. One of the issues they addressed was whether a dictionary records present usage of the language or provides a reference for the correct usage of the language.
The problem with the former is that there becomes no correct way to use the language, and it can mutate unchecked. It was after all the invention of the dictionary that made so texts could still be understood centuries later.
On the flip side, there is obviously no way you can have a static language. There need to be new words for new inventions — telephone, internet, neutron star, etc. I would argue that we should let our language evolve even more than that. A language defines how we think. If you look at different cultures, they litterally have different concepts they can express. So in that way I think natural language is kind of like programming languages. Yes there is a place for assembly or C, but higher level languages are so much more expressive. A large fraction of how software keeps getting better is by people using these more expressive languages. So have to think that there is some sort of parallel to the evolution of natural language.