There hasn't been a lot of focus on Maria Hill appearing in The Avengers. With so many other characters, it's easy to do. In the comics, we've seen her character take on an important role. The question is, how much action will she see in the movie. From the few images we've seen, it's looked like she was only going to be sitting or standing behind a computer terminal.
Last night Cobie Smulders was on Late Show with David Letterman. A clip from the movie was shown and while it doesn't show an extreme amount of action, she is getting away from that computer terminal.
Hopefully she'll get to see some of the big action in the movie. But with all the other characters, it's easy to see how Maria Hill could get lost in the shuffle. Perhaps if we ever see that Nick Fury/SHIELD movie, there'll be a bigger role for her. There's also that old rumor that used to be listed on imdb. Maybe that will happen.