From experience I can say without reservation that sex.com's traffic is TOTAL garbage. My best guess is that when they hit their peak a few yrs back they took on "partners" (much like Overture) that are essentially spam sites or worse. Overture buys garbage domains like those below:
http://www.7xxx.com
http://www.uxxx.com
http://www.sexfu.com
(See a pattern here? And you pay the same click charges on these as you do on Yahoo, etc.)
Back to the point, I think sex.com has taken on the same approach, though I don't have examples from my logs. In any event, conversion rates are absolutely pitiful.