We have seen Scarlett Johansson as the black widow in Iron Man, but what does her role have to do with The Avengers or Spider-Man? In short everything. The Black Widow is a important part of the Marvel Universe. She is everywhere. Whether or not she will appear in The Avengers remains to be seen but according to Scarlett:
"I hope I get to come back and do it again," she said. "The character certainly comes back. We see that she does in the comics and certainly she is a big part of The Avengers. I don't know if that is where it's going to go but she is definitely a big part of The Avengers."
Should Johansson's Black Widow join The Avengers to fight along side Tony Stark(Robert Downey Jr.), Nick Fury(Samuel L. Jackson), Thor (Chris Hemmsworth), The Hulk (Edward Norton), and the still un cast Captain America? My answer is yes. Marvel would be crazy not to have her in The Avengers. Sony is crazy not to have her in one of the upcoming Spider-Man films. Regardless of what studio owns what property, money talks and BS walks. If the studio's think they will profit then we will start to see crossovers. Like I said above if you have read the comics Black Widow is everywhere and that needs to be reflected in the movies if they are to mirror the source material. I would much rather see Scar Jo in The Avengers then in her own stand alone movie.
Scarlett Johansson goes on to say:
"She (Black Widow) has many different incarnations and different storylines so I'm hoping she will be able to continue in that way," states the actress. "I'm hoping that if the fans like the character and support the character, we'll see her again."
Oh yes, we will see you again Scarlette.