Some researchers attached sensors to 101 penises and then showed the possessors of these penises either all-male or all-female porn movies. It was kind of a lie detector test, because the men had all professed to being heterosexual, homosexual, or bisexual. All the bisexuals, it seems, were lying -- or deluding themselves. Once you disregard the one-third of men who weren't aroused by any of it -- which, rightly or wrongly, the scientists do -- all the men were distinctly attracted either to males or to females. This contradicts the views of Freud (who thought bisexuality was the norm) and Kinsey (who thought there was a continuum from heterosexuality to homosexuality).
I think you can critique the study in various ways, but I'm also interested in how this finding -- if we were to confirm it as a solid fact and applicable to women as well as men -- would affect various arguments about gay rights. Let me posit that believing Kinsey was right about the continuum is currently causing many people to resist the social acceptance of homosexuality. They are hoping to influence people in the middle of the continuum to choose a heterosexual "lifestyle." But if no one really is in the middle, this attempt at influence is truly misguided. You may as well remove the obstacles to the individual's free choice of sexual orientation.