I think it's charming, but not especially surprising, that the role Jane Lynch just murked in The 40-Year-Old Virgin was originally written for a man. Movies like that, and like Salt, where Angelina Jolie is playing a character initially written for Tom Cruise:
Should really go some way towards making directors, producers and writers assess how gender-determined certain roles actually need to be. There are some situations where it obviously make sense to have certain characters played by men or women. If you want to explore a woman's attitude towards pregnancy, or a man's attitude towards towards the particular gender roles and expectations foisted on early-21st-century men, you can't easily make substitutions with the gender of the actor. But if someone is a spy motivated by concern for their family, the manager of a general-interest retail store, a tough lawyer working a hard case, or any number of other roles where gender is not the key subject the movie is exploring, then there's no absolute need to cast men and women in certain kinds of roles.
And I think gender-neutralizing certain kinds of roles could also broaden the range of physical appearances folks can have and still make it in the movies. One of the things I find interesting about Angelina Jolie's immense physical beauty is that even though she's quite thin, and while she's toned, is definitely not ripped, is that her wildly exaggerated femininity doesn't translate into weakness for most viewers. She's turned those looks into the plausible tools of an action hero. Conversely, someone like Lynch (who is gay) might be stereotyped into plain-lady or lesbian roles because she's tall, has short hair, is not visibly particularly curvy. But she gets cast as someone's heterosexual mom in Post Grad, Julia Child's surprisingly sexy (and also hetero) sister in Julie & Julia, the fearsome grandma in Talledega Nights, and the sort of omni-manipusexual in Glee. We need more diversity of all types in movie: of place, of narrative, and of actors. In their own weird ways, both Jolie and Lynch are pushing that cause forward. One can only hope the rest of the industry will get in line behind them.