Believe it or not, but while it's been a several months since it became clear and generaly accepted that Joss Whedon was the man who had been hired to direct the Avengers, neither he nor Marvel have actually put anything on the record to confirm that. Now that's changed, as Whedon pitched up at the Visionaries panel at Comic-Con, saying that "I am directing The Avengers".
However even here he prefaced it by joking, "That's not an official thing, probably because Marvel can't afford a press release." The reason for the secrecy is that it's believed that during the Marvel panel on Saturday, the comic company wants to go for the big reveal, where Whedon will be wheeled out and officially announced as director, along with all the major cast members - including Ed Norton's replacement as Bruce Banner/Hulk.
Apparently the director is still at the stage of outlining the script, adding "It's totally counterintuitive. These people should not be in the same room together, let alone on a team, and that to me is the definition of family." Expect to hear more on Saturday.