As Kat Ño said, it is very difficult to have data on Esperanto speakers based on more than personal anecdote. In my experience, though, the events I have attended were pretty gender-balanced, but there were probably a little more men than women. I had a look at the lists of people who registered to Somera Esperanto-Studado in the last years, and the percentage of women is around 45%. On Lernu.net, however, 55304 registered users are female, while 91704 are male, which makes 37.6% of women. I don't know if this figure is more representative or if it shows that Lernu appeals more to men or something else.
I've also read a claim in the Lernu forum that most American Esperanto speakers are men, while most Russian Esperanto speakers are female.