As a woman in IT since the 80's, I can confirm that there is a lot of sexism, and it does impact the paycheck as well as the work you are assigned and the recognition you get.  (My current company is the first exception to that rule of IT, which is one of the reasons I stay here!)

We're even seeing some of that sexism in this thread, even beyond the "females are more nurturing" (as though that had anything to do with programming talent or desire for a high-tech career).  And it wasn't just men who created computers and computing languages, although as usual they get the credit.  Go back and find out who wrote COBOL, the main business programming language for the last five decades.  I believe Commodore Grace was a WOMAN (and I can confirm this because I saw her speak prior to her death).  The original programmers were mostly women, because that's who knew how to type!  Go check out the history of computers - you may learn or re-learn some interesting facts about gender roles in early IT.

There are a huge number of assumptions related to IT that just are not true.  I don't think of myself as a "geek", nor do other people call me one.  I am an intelligent, well-read woman who enjoys working on her own cars and motorcycles - so some days I'm typing code with bandaides on my knuckles!  Give up the stereotypes, people.  Anyone with the skills can suceed in IT.  But young girls are not encourage, and in fact are still actively DIScouraged from taking on careers (or hobbies) in fields that are seen as male-oriented.  And a discouraged person will not perform well (yes, that's a pun!)

Is any of this a reason that the numbers of women in IT are dropping?  Possibly, but until someone does a real study that asks women why they are leaving, or not entering the field, we won't know for sure what is driving it.  One of the reasons I chose IT as a career path was because it was a relatively new arena, with lots of growth potential.  Biopharm and Biogenetics are the next big up-and-comers, so it's not surprising that young people are more interested in those as careers.  But the drop in percentages of women entering IT indicates to me that there is probably more than one driver for the drop in numbers.  (And BTW, numbers ARE important - they are a way to measure what we experience.)