Interesting study:

The genitals of the volunteers were connected to plethysmographs — for the men, an apparatus that fits over the penis and gauges its swelling; for the women, a little plastic probe that sits in the vagina and, by bouncing light off the vaginal walls, measures genital blood flow. An engorgement of blood spurs a lubricating process called vaginal transudation: the seeping of moisture through the walls. The participants were also given a keypad so that they could rate how aroused they felt.

The men, on average, responded genitally in what Chivers terms “category specific” ways. Males who identified themselves as straight swelled while gazing at heterosexual or lesbian sex and while watching the masturbating and exercising women. They were mostly unmoved when the screen displayed only men. Gay males were aroused in the opposite categorical pattern. Any expectation that the animal sex would speak to something primitive within the men seemed to be mistaken; neither straights nor gays were stirred by the bonobos. And for the male participants, the subjective ratings on the keypad matched the readings of the plethysmograph. The men’s minds and genitals were in agreement.

All was different with the women. No matter what their self-proclaimed sexual orientation, they showed, on the whole, strong and swift genital arousal when the screen offered men with men, women with women and women with men. They responded objectively much more to the exercising woman than to the strolling man, and their blood flow rose quickly — and markedly, though to a lesser degree than during all the human scenes except the footage of the ambling, strapping man — as they watched the apes. And with the women, especially the straight women, mind and genitals seemed scarcely to belong to the same person. The readings from the plethysmograph and the keypad weren’t in much accord. During shots of lesbian coupling, heterosexual women reported less excitement than their vaginas indicated; watching gay men, they reported a great deal less; and viewing heterosexual intercourse, they reported much more. Among the lesbian volunteers, the two readings converged when women appeared on the screen. But when the films featured only men, the lesbians reported less engagement than the plethysmograph recorded. Whether straight or gay, the women claimed almost no arousal whatsoever while staring at the bonobos.

Source: http://www.nytimes.com/2009/01/25/magazine/25desire-t.html?scp=1&sq=&st=nyt&pagewanted=all&_r=1&

Overall, the article is pretty much a must-read, it helps clarify a lot of things said on TRP. For example, here's a good quote:

The generally accepted therapeutic notion that, for women, incubating intimacy leads to better sex is, Meana told me, often misguided. “Really,” she said, “women’s desire is not relational, it’s narcissistic” — it is dominated by the yearnings of “self-love,” by the wish to be the object of erotic admiration and sexual need. Still on the subject of narcissism, she talked about research indicating that, in comparison with men, women’s erotic fantasies center less on giving pleasure and more on getting it. “When it comes to desire,” she added, “women may be far less relational than men.”

Like Chivers, Meana thinks of female sexuality as divided into two systems. But Meana conceives of those systems in a different way than her colleague. On the one hand, as Meana constructs things, there is the drive of sheer lust, and on the other the impetus of value. For evolutionary and cultural reasons, she said, women might set a high value on the closeness and longevity of relationships: “But it’s wrong to think that because relationships are what women choose they’re the primary source of women’s desire.”

Meana spoke about two elements that contribute to her thinking: first, a great deal of data showing that, as measured by the frequency of fantasy, masturbation and sexual activity, women have a lower sex drive than men, and second, research suggesting that within long-term relationships, women are more likely than men to lose interest in sex. Meana posits that it takes a greater jolt, a more significant stimulus, to switch on a woman’s libido than a man’s. “If I don’t love cake as much as you,” she told me, “my cake better be kick-butt to get me excited to eat it.” And within a committed relationship, the crucial stimulus of being desired decreases considerably, not only because the woman’s partner loses a degree of interest but also, more important, because the woman feels that her partner is trapped, that a choice — the choosing of her — is no longer being carried out.