I think Fran Allen (the only female interviewee in Coders at Work) made the point that you see more and more women going into Earth Sciences, Biology, Chemistry... Even Engineering and Maths have more balanced gender ratios than CS. Her opinion was that it was because those fields are perceived to be more socially relevant, wheras a lot of people think CS is just about making games.

I don't know if I agree with her totally (I think the negative perception is more a conflation of IT with CS - people think CS is more about using Powerpoint than an intellectual pursuit) - but there is definitly a case for fixing the public perception of Computer Scientists.