I've watched quite a few documentaries about polygamous relationships, and often wondered if I was in the minority thinking that it's not necessarily a bad thing. As others have said, as long as it's between consenting adults I don't see why it's a problem - in fact I can see quite a lot of benefits to the idea. For one, there are more adults to share the housework/childminding duties; as far as the kids are concerned, the chance of getting a "I'm too busy to help you right now" response would be drastically reduced; there will always be someone you can talk to if you're having problems; and if one of your partners is too tired/has a headache/is pissed at you for something, you don't have to share a bed with them.
I don't plan on ever getting married so it doesn't really affect me in any way, but if it works for you, have at it!
I don't plan on ever getting married so it doesn't really affect me in any way, but if it works for you, have at it!

"No-one who decides that scientific evidence is not for him and that his own experience or the stories of others is the be all and end all of deciding what's true ever has the right to call people searching for reliable, repeatable evidence narrow-minded. That is hypocrisy of the most laughable kind." Derren Brown - Tricks of the Mind.