To attempt to answer this thread (and double post in the process), i found this on Yahoo! Answers (which is one of the few things Yahoo really does well)
Comes from a user with some name full of Greek letters
The average ratio from seven major studies (The prevalence of homosexual behavior and attraction in the United States, the United Kingdom and France: Results of national population-based samples - Sell, Wells, and Wypij; The Social Organization of Sexuality: Sexual Practices in the United States - Laumann, Gagnon, Michael, Michaels; The Janus Report on Sexual Behavior - Janus and Janus; Homosexuality/Heterosexuality by McWhirter, Sanders, and Reinisch;
The Kinsey Date - Gebhard and Johnson; Sexual Behavior in the Human Male - Kinsey, Pomeroy, and Martin; Sexual Behavior in the Human Female - Kinsey, Pomeroy, Martin, and Gerhard) are that 9.61 percent of men are homosexual and 4.58 percent of women are homosexual. The Laumann et.al. study had the closest percentages (7.7 percent gay men to 7.5% percent lesbian women) while the McWhirter et.al. study had the widest disparity (13.95 percent gay men and 4.25 percent lesbian women), but these studies only report their findings without asking the question as to why there are more male homosexuals than women homosexuals. Studies that have asked why people are homosexual usually use male subjects. To my knowledge, studies on the causation of male homosexuality in relation to causes of female homosexuality has not been studied.
My opinion, based on what I have read and seen, is that male sexuality is more driven by visual images. This is why most "adult entertainment" is geared towards men. Both straight women and gay men stereotypically use several personal care products which can be advantageous when trying to find a partner who is more visually driven.
On the other hand, female sexuality is more driven by emotions. Instead of "adult entertainment" women prefer love letters and romance novels. Women tend to care more about the person than the body that they are in. For this reason, there may be more female bisexuals than male bisexuals, with the percentage of both gay and bisexual men and the percentage of both gay and bisexual women being close to the same percentage. If 10% of men are gay and 5% of women are gay, but 5% of men are bisexual and 10% of women are bisexual, there would be 15% GLB men and 15% GLB women.
http://answers.yahoo.com/question/index?qid=20081102115135AAtP7nU
This seems to answer the question well.
