I like this article because it points out women are also geeky and that it's OK to be geeky. Women just may tend to have a slightly different way of expressing that geekiness.

You want girls to feel comfortable because you want the girls who are good at CS to go into CS. This is independent of how many women go in total. But since we're at it, let's talk about the biology arguments:

http://geekfeminism.org/2009/10/17/how-does-biology-explain-...

http://www.mun.ca/cwse/Cannon,Elizabeth.pdf

according to the above study, undergraduate women in engineering showed comparatively a higher interest in math than men though slightly lower interest in engineering and yet lower interest in physics.

http://www.cs.cmu.edu/afs/cs/project/gendergap/www/papers/

Through additional work CMU increased their percentage of women in CS from 8% to 1995 to 42% in 2000. One thing I recall is that women were not as experienced when they first got into CS and had to work harder. However they believed they had caught up by junior year.