This is mostly just brainstorming/train of thought stuff so it might not be totally coherent. I was thinking about how my next computer will be built by me, and got to wondering why more women aren't into "geeky" things, and realized it's more that women aren't into technical geeky things. There's quite a few women into media-geeky things, like sci-fi, fantasy, anime... the more technical you get, though, the less women there are. Less women are into video games, even less into roleplaying or tabletop gaming, very few into computers and technology, and even less than that are into hard sciences or advanced math. Women are just as capable of this stuff, so why the gender gap?
Some possible reasons:
-Little girls are much, much less likely than boys to receive things like Legos and video games as gifts, and toy store displays and toy commercials tend to reinforce this. I loved the idea of Legos as a little girl, but would never have thought to ask for them because they were in the "boy aisle" with things like G.I. Joes and whatnot, and were usually covered with pirates, firemen and other things that focus on male-oriented roleplay. I did have video games, but I got the sense that most other girls my age didn't think they were cool. I don't think the solution is to cover Legos in pink unicorns, but simply to offer more unisex options rather than marketing directly to boys. I do think video games are fairly unisex and the gender gap there puzzles me, so I can't comment on that as much.
-Little girls are also less likely to be involved in what is stereotypically seen as "dad work": often dads include their sons in things like repairing the car, building things, or fixing things around the house - all of which build math, science, and technical skills - but might not think to include their daughters. Partly this is a bias in the collective unconscious of Americans about what work is appropriate for either gender, and partly it has to do with little girls being more protected from injury, etc. Both attitudes are sexist, but are usually not done with the conscious intention of depriving girls; they're oversights due to culturally ingrained messages that are unfortunately slow to change.
-Women are frequently driven away from roleplay-type gaming (WoW, D&D, etc) by sexist attitudes among male players; often these games are for whatever reason like a boys' club and there is an air of talking down to women. This is unfortunate as this again is another area which is rife with opportunities to gain mathematical and technical knowledge, plus more girl geeks = more guy geeks with girlfriends. Everyone would win!
-The rarity of girl geeks is perhaps self-perpetuating, as men become accustomed to having few women around and may rush to get the attention of females who join their activities. Being deluged with unwanted advances makes women uncomfortable; thus, they leave.
These are just a few ideas; I don't pretend to have it all figured out. Certainly there are many, many factors. But these are the ones that, in my own experience, have kept *me* away from some technical/mathematical things I might otherwise enjoy.