The problem that I see in poly relationships, alot of the the time the participates are not getting the same amount of satisfaction. When that happens, believe me, the relationship can unravel so quickly. The other point I wanted to make is alot of people are very jealous/possessive of their significant other. That is a recipe for disaster in this type of relationship. It takes very special people to participate in a poly relationship. You have to be willing to share and put your partners needs before your own.
I do not agree with that last sentiment. Everybody should have their needs met, that is the whole idea. Often that means that a couple both have other lovers/significant others, or that a family loves all around. The point is more to everybody, not less. As I see poly.