I'm skeptical because of the huge differences in male and female dominant strategies for mating*. I think poly can work, but that a lot of people who consider themselves poly just haven't run into a highly frictional situation yet or have put their fingers in their ear and are shouting "lalalala".

*I should note that I'm also extremely skeptical of monogamy. The situation that makes men and women happiest seems to involve some (sometimes a lot) of unhappiness in their partners.