I find it amazing that it has been more than 40 years since Alice Bradley Sheldon donned the pseudonym of James Tiptree Jr. and launched herself into the Science Fiction world. In that time, we have seen a lot of culture changes, and these days the thought of women writing SF is hardly worth batting an eyelash... or is it?
On the one hand, we still have many female authors obscuring their names through the use of initials or misleading nicknames. I would have thought that the need to cloud an author's gender was way behind us, but apparently there are still ignoramus-es out there who will staunchly not pick up a book by a female author. Still, authors like C.J. Cherryh, S.L. Viehl, and Rob Thurman may have a point: it looks like their sales are higher than average (though I personally suspect that this has more to do with the fact that they are all amazingly gifted writers).
On the other hand, take a walk down the Science Fiction and Fantasy section of your local book shop and look at the names of the authors. Sure, the field is still dominated by men, but not by that wide a margin. In fact, I would be willing to bet that we are closer to parity in the genders in the genres than anywhere else in the market! One thing is sure: if you add in 'Paranormal Romance' to the traditional SF lists, it is likely that there are more females than males writing SF these days.
I am all for diversification, and frankly I look forward to the day when this is no longer even an issue. Hopefully, in some Gene Roddenberry utopia, we will no longer check to see is an author is male or female, black or white, gay or straight. When I wake up in that future, it will be glorious!