I just know this is going to generate a lot of discussion!
In the first three months of 2007, according to Nielsen/NetRatings, approximately one in three visitors to adult entertainment Web sites was female; during the same period, nearly 13 million American women were checking out porn online at least once each month.
Theresa Flynt, vice president of marketing for Hustler video, says that women account for 56 percent of business at her company's video stores. "And the female audience is increasing," she adds. "Women are buying more porn." (They're creating more of it, too: Female director Candida Royalle's hard-core erotic videos, made expressly for women viewers, sell at the rate of approximately 10,000 copies a month.)
http://edition.cnn.com/2009/LIVING/personal/07/24/o.women.watching.porn/index.html
Note the source (CNN republishing an article from O Magazine)...if Oprah's magazine is reporting on porn, then for better or worse it's arrived in the mainstream. So if the article isn't correct now, it might be soon.