Good question. There's no question that academic philosophy has some influence on society, like law, applied ethics, etc. But if you're talking about the ordinary lay person, I believe that academic philosophy has very little influence on their thinking. The philosophers of the enlightenment probably had the most influence on society. It's very hard to say which reflects the other. Maybe it's a chicken or the egg kind of thing.

From what I understand during various socio-history and anthro-history classes. Academia reflects the edges of a society, the fringe, those people not represented in the middle or the 'average joe'. However being on the intellectual fringe and endowed with an abundance of social prestige giving them a disproportionate sway on public opinion, it often means that academia is the vanguard. Society often eventually goes where academia has already been. Sort of like an overblown intergenerational Kuhnian paradigm shift. Not being a historian I can only attest to the same sort of model being implemented in endangered languages, yet at this point I have no real reason to discount what my professors said so many years ago.

Philosophy does not exist in a vacuum somewhere in the groves of academe. Consider, for example, its interaction with science, especially since Bacon, or consider its influence on the American Revolution. Generally, though, it seems that the influence is less than direct and immediate, but filtered or mediated before it becomes an effective motive of action (consider the Industrial Revolution from about 1830 to 1930). In this process, it somewhat resembles the mediation of technology to the discoveries of pure science.

The Summa to Roman Catholicism
The Second Sex to the Women's Movement
Das Capital to Communism

All of these significant texts can be seen as an reflection of the concerns of society, of the circumstances in which they were written, and---at the same time---they helped shape subsequently the views of society, but different ways.

My point is that the relationship between Philosophy and Society is extremely complicated, and not always am obvious and direct causal one, just as language both shapes and reflects the society at any one time.

A very interesting question, though. Very interesting.
Regards,
John