There is a lot more butt sex taking place

Experimentation, orgasms, and the rise of anal sex. - By William Saletan - Slate Magazine

Looking more carefully at orgasms and anal sex:

Only 6 percent of women who had anal sex in their last encounter did so in isolation. Eighty-six percent also had vaginal sex. Seventy-two percent also received oral sex. Thirty-one percent also had partnered masturbation. And the more sex acts a woman engaged in during the encounter, the more likely she was to report orgasm. These other activities are what gave the women their orgasms. The anal sex just came along for the ride.
So why did the inclusion of anal sex bump the orgasm figure up to 94 percent? It didn't. The causality runs the other way. Women who were getting what they wanted were more likely to indulge their partners' wishes. It wasn't the anal sex that caused the orgasms. It was the orgasms that caused the anal sex.
If anal sex is a trailing indicator of women's sexual satisfaction, then by all means, let's toast the new findings. Here's to you, ladies. Bottoms up.