Sex addiction seems to be popping up all over.

Actor David Duchovny checked into a rehab facility for sexual addiction in August -- just before the new season of his randy TV series "Californication." In her new book, "Desire: When Sex Meets Addiction," Susan Cheever recounts having sex with men she barely knew at times of stress: "Moving men, doctors, lawyers, book salesmen -- any man associated with a threatening change in my life became erotically charged, with predictable results."

But is sex addiction a real disease, or just an excuse for behaving badly? How much is too much? When does preoccupation cross the line into pathology?

The psychotherapy community has been wrestling with such questions for years.

One camp thinks the very notion of "sex addiction" implies a narrow, moralistic view of what's acceptable. "There are millions of people stuck in unhappy relationships who go to massage parlors or the Internet and to demonize their sexuality is terribly unfair," says Marty Klein, a licensed marriage and family therapist and certified sex therapist in Palo Alto, Calif. He says people who are unhappy with their sexual choices may be depressed or bipolar or need to face the fact that their relationships have failed, but the problem isn't necessarily sex.