Re: AVENGERS: Grade, Reviews, Discuss, DVD & Sequel **SPOILERS**
It's pretty clear from the movies and hints in them that Iron Man 2, TIH ad Thor all pretty much take place at the same time. (In Iron Man 2 in the SHIELD office at the end footage of the battle with Hulk at the University can be seen on one of the screens, also in the movie Coulson mentions going on a mission which the end-credits scene shows was recovering Mjolnir in the desert.)
Iron Man is obviously the earliest point in the MCU (other than, of course, the 1940s time period of CA and the BCE portions of Thor.) The only movie that's hard to "peg down" is Captain America as there's no much to clue us in on when he woke-up in present day.
All we know is that Cap was found one year after all the other movies (per Fury's Big Week
), which would be May 2011.