This is a growing practice in my area. I know several couples trying it out, with various success. TONS of therapy for all of them. It's more like therapy has become a new hobby to go along with their expensive dates that split time throughout the week, and split attention when together.
Not saying polyamory isn't totally possible and perfect for some people. But when polyamorists marry monogamists, it seems like no matter how hard the monogamist tries to be game, their wiring never really gets rerouted into being okay with their spouse being poly (although they seem to be the ones okay with having multiple partners themselves...their partner just can't).
But, hey, there's a learning curve in all things, right? I pretty sure more and more people will start trying polyamory in the future. No one I know who has opted in has opted back out. So there's that.
RE: My Top 5 Reasons: Polyamory