Say you're an expert in psychology with heavy philosophical leanings, and you find yourself getting interested in the theories of Husserl and Heidegger. Like, really interested. To the point where you begin to see the scientific results of the psychology and biology of your day as actually confirming the rich descriptions and the highly textured world of the dudes from Freiburg, against the sorts of (dualist, physicalist, behavioralist...) metaphysical assumptions tending to undergird those scientific investigations themselves.
Let's say you're also working in France, just after the war. Most of what your colleagues know about Husserl and (particularly) Heidegger, they know through Sartre's recently published and hugely famous Being and Nothingness - which, while interesting, is not a particularly canonical presentation of Husserl's phenomenological project. You want to develop your own work in the field, but how to provide a context for it? How to introduce and sum up half a century's worth of a philosophical tradition for your countrymen, in such a way as to make it not only philosophically interesting but scientifically relevant?
And that's how the world got the "Preface" to Merleau-Ponty's Phenomenology of Perception. The PoP as a whole is now considered a classic of 20th century philosophy, and (through Dreyfus and others) has been hugely influential in recent philosophy of mind and related areas. But the "Preface" is a masterpiece all its own. Maybe it's not quite as infamous as the prefaces to be found in Kant or Hegel, but really: go around looking for an introduction to this crazy movement called "phenomenology," and you're still not likely to find better than what Merleau-Ponty penned nearly 70 years ago. And for a 15-20 page chunk of text, that's pretty remarkable.
So! Now that there's a new and improved translation of the PoP out as of last year, let's get together and get ourselves stuck into this little wonder. I'll scan and post the new Landes translation sometime in the next couple of days, although (as I recall) the old Smith translation wasn't too bad (at least for this portion of the book).
EDIT: And here's the file: http://files.meetup.com/1470198/M-P%20Preface.pdf