Well, It turns out he was part-right, as it is more of a single "shot" that appears at the very end of the credits. The first post credit scene comes fairly early after the main movie ends. To see the contents of that: Be warned though, this moment is best left for a first viewing on the big screen.
Now, about that second post credit sequence. While the information below isn't necessarily a "plot spoiler", you will surely not get the reference until you see the actual climax of the film itself. If you want to retain the surprise, read on at your own risk. Those outside the US, and those lucky enough to have seen the movie at an advanced screening that did not contain this recently shot parting zinger, may want to read on (we've also included a photo).
The shot is a call-back to something Tony Stark (Robert Downey Jr.) says moments after the big final climax of the film. If you've read this far and are squinting your face, you'll get it once you see the movie. Trust us, its not product placement.
Marvel's The Avengers was released May 4th, 2012 and stars Robert Downey Jr., Chris Evans, Mark Ruffalo, Chris Hemsworth, Scarlett Johansson, Jeremy Renner, Tom Hiddleston, Clark Gregg. The film is directed by Joss Whedon.