I'll need to find some statistics to back these assertions up, but let me give you my initial opinion on a New Scientist article linking smoking with teenage lesbianism and bisexuality. [Update: This post is really meandering; I can't collect my thoughts for some reason.]
Teenage lesbian or bisexual girls are many times more likely to smoke regularly than straight girls their age. They are the worst hit by tobacco among all groups of young people, according to a new US study.The connection seems obvious to me based on prior reading and anecdotal evidence (follow those links at your own risk). The mechanism that leads some young women to experiment sexually with other women is apparently somewhat different from the mechanism that leads men to have sex with men.Almost 40 per cent of teenage lesbian or bisexual girls aged between 12 and 17 said they smoked weekly compared with just six per cent of heterosexual girls in an ongoing study of 16,000 adolescents.
As Clayton Cramer has pointed out many times, there's a strong correlation between male homosexuality and prior childhood sexual abuse, but I haven't seen much evidence to suggest that sexual abuse as a child affects women the same way. Sexually abused girls tend to have serious emotional and sexual problems as adults, but they don't tend towards homosexuality any more than girls who experience other childhood stressors, such as divorce, social ostracism, and so forth (from what I've read, and considering that girls are more likely to be abused in general than boys).
Women who have sex with women (WSW) comprise 20% to 30% of injection drug users (IDU) according to a study in the American Journal of Public Health (via Mr. Cramer). The study doesn't mention the prevalence of male homosexuality among IDUs, but I'm assuming it's less than 20% -- otherwise the results for WSW wouldn't be interesting. Considering the links between smoking and drug use in general, it's not surprising that young lesbians tend to smoke a lot; I bet they also drink considerably more than their straight peers.
So what's the deal? As Dan Savage's correspondents indicated, many "lesbians" are attracted to men and only "experimenting" with women. Men generally have sex for pleasure (with procreation only as a side-effect), and I'd assume that can be had with partners of either gender; women ultimately have sex to procreate, so they often return to being straight even after experimenting with homosexuality.
It appears that for women, experimenting with homosexual sex is similar to experimenting with drugs and alcohol, whereas for men it isn't. Childhood sexual abuse seems to strongly correlate with male homosexuality in a way that other stressors do not -- for instance, socially ostracized males aren't any more likely than average to become homosexuals, even though they are more likely to experiment with drugs. But these other stressors do seem to encourage young women to experiment with lesbianism, and when (if) they grow up past the stressors they discard lesbianism along with the rest.
I've actually had several friends in the 19/20 age range proudly declare they are lesbians, hook up with another girl aprox. the same age, and by the time they were 25 were married to a guy. I've never witnessed similar in the male population. It's a topic I've discussed a few times with other people, but we've never come up with a good explanation as to why.
It's "cool" to be a lesbian nowadays. It's trendy. It gets you attention. It's a quick and easy way to make you "special" and get people to offer you all sorts of opportunities. For boys, however, being gay isn't cool.