I recently watched The Hobbit, and it seems they added a female character (just for a few minutes) only so that there would be at least one woman character in the movie...
This reminds me of the Bechdel Test and click here for overall statistics. The criteria are simple, movies are divided into four groups along whether they pass one or more of the following criteria: 1. It has to have at least two [named] women in it
2. Who talk to each other
3. About something besides a man
For more on female heroines in movies see the recent article in the NYTimes Magazine.
For stats on female scientists see the following Slate Article, and a slightly dated short summary plus compilation of links at "Female Scientists on the Big Screen".