New York Magazine says that buttlove is the new oral sex for heteros:

38.2 percent of men between 20 and 39 and 32.6 percent of women ages 18 to 44 engage in heterosexual anal sex. Compare that with the CDC’s 1992 National Health and Social Life survey, which found that only 25.6 percent of men 18 to 59 and 20.4 percent of women 18 to 59 indulged in it.

Anecdotal research also demonstrates curiosity is on the rise. Babeland’s anal-sex workshops are now held three or four times a year, instead of once, and they’re filled with straight couples. “More and more, people are devoting themselves to learning about anal pleasure,� says Carolyn Riccardi, education coordinator for Babeland’s New York retail stores. “Male-to-female anal sex has been happening since the dawn of time,� she says. “What’s different now is that women are actively learning how to enjoy it and have fun with it.�

I'm willing to believe that Sex and the City and the ubiquitousness of porn has convinced a lot of women that guys will think they're uptight and unsexy if they don't do all this stuff - and they're pretty much right, I guess.

But I also doubt that there's been THAT much of an increase in this activity; it seems more likely that women are now less bashful about admitting that they do this stuff, or would be willing to lie and say they're into it when they're not (see above re not wanting to be perceived as uptight and unsexy).

That said, over the last several years, chastity pledges ("True Love Waits" and their ilk) seem to have made anal sex popular amongst teenage girls who think that taking it up the ass doesn't count as sex. From Bill Maher (via Amy Alkon):

A new eight-year study just released reveals that American teenagers who take "virginity" pledges...wind up with just as many STDs as the other kids. But that's not all -- taking the pledges also makes a teenage girl six times more likely to perform oral sex, and a boy four times more likely to get anal...[A]rmed with limited knowledge, and believing regular, vaginal intercourse to be either immaculate or filthy dirty, these kids did with their pledge what everybody does with contracts: they found loopholes. Two of them to be exact. Which leads me to an important question: where were these pledges when I was in high school?

Seriously, when I was a teenager, the only kids having anal intercourse were the ones who missed. My idea of lubrication was oiling my bike chain. If I had known I could have been getting porn star sex the same year I took Algebra II, simply by joining up with the Christian right, I'd have been so down with Jesus they would have had to pry me out of the pew.