When I did it seven years ago I didn't get a stamp, just a paper.
That paper I later left at my parents place in Sweden on our return trip and Air France wouldn't let me back on the flight. My parents had to fax it through to the office in Paris for us to be allowed to enter the plane. At Ezeiza we didn't have any trouble. Then they sent all the documentation with FedEx.
If I had had a stamp in the passport I wouldn't have had all that trouble...