I'm not in computer science, but I've been in network administration for going on 16 years now. I also consulted for a few years during that 16 years.
I've met hundreds of men in the field, and I'd have to say the bulk of them were competent, at least to some degree.
I've met less than a dozen women in the field, and two of them were competent.
I don't know if my experience is indicative of the rest of the field, or of other areas in the broad computing-related disciplines.
However, my observation has been that in order to be successful in networking and computing, you have to be able to think logically. Sure, you can excel if you have a good memory, have lots of experience, or are very intelligent, but to be minimally competent, you have to be able to think logically.
I just haven't come in contact with many women, both in the field and out, who can or will think logically on a consistent basis when solving problems.
In other fields, this isn't a problem, and in the creative fields, it can probably be a detriment. I've met a lot of very creative women in web design, for example, who can do some amazing things. I've also met some great women who excel in project management and organization - something with which many technical guys are sorely lacking (myself included).
In my narrow area of the field, where supporting critical systems is the bulk of the job, part of the work includes scheduling regular maintenance during off hours, and responding quickly to outages or problems. Most women (in my experience) aren't willing to work these sort of hours, or can't because of family commitments.
Put the two together, and it effectively rules most women out of the field. Its not a question of not being able to do it from an absolute perspective, its a question of not willing to do what it takes to be compentent, and not willing to do what it takes to be available. Its a choice, just like any other, and most women don't seem to want to choose to do what it takes to be a part of the industry.
Just my humble observations.
bingo