[NSFW?] What is your opinion of open relationships?

After watching an interesting program about one particular married couple, in regards to open relationships. I do feel there is some merit.

Their premise is basically total honesty, never bail or leave the committed relationship, and fear and guilt should not form part of their unison.

Along with the couple were the other people they had gathered due to having relationships with, all intertwined and all in love with various members of this micro community. Jealousy was discussed, but how can there be jealousy if you never leave for another? Do you feel this is an option you would consider at all? What for you would be the upsides and downsides of such a decision?