One of the articles I read at Borders yesterday in The Advocate was written by the first openly gay psychiatrist in the American Psychiatric Association. I didn't commit his name or exact quotes to memory so I'm going to paraphrase a lot here, but he has come out with a new book in which he advises gay men to "strive for" monogamy in their relationships.
He said that he believes as children, gay men deal with the threat or reality of family and friends turning against them and therefore grow up to be adults that don't fully trust other people. He said that "open relationships" are a symptom of that lack of trust, because the partners are 1.) on some level refusing to commit to each other, 2.) are purposefully establishing rules that naturally inject some form of doubt into the relationship, or 3.) are refusing to believe that they can be fully satisfied by having a deep and still dynamic relationship with one person.