This is NOT the first time this has happened, but Helen Hunt is playing the Stage Manager in Our Town off broadway right now, a role usually played by a man. Which is awesome.
I tried to do this earlier this year, in a local production of Willy Wonka. They posted a message on a local forum that they needed more adults for the show, so I called the director and asked if I could come to callbacks and audition for the role of Willy Wonka. Any guesses about what she said?
Admittedly, this was a very small theater, and it tends not to try anything too "out of the box." I was still pretty disappointed; how cool would that be?? At least Helen Hunt gets to live my dream.
Go read all about it here.