- Mo'Nique & husband Sidney Hicks (although Mo'Nique says she doesn't do any straying)
- Angelina Jolie & Brad Pitt (although the "more conservative" Pitt is not polyamory-friendly) (pictured right)
- Will Smith & Jada Pinkett Smith (with approval from the other) (pictured below left)
- Megan Fox & boyfriend Brian Austin Green (although not a mutually-open relationship)
- Tilda Swinton & partner John Byrne (both have a lover outside of the marriage)
- Justin Timberlake & Jessica Biel (although it sounds like Biel isn't fully happy with the situation) (pictured far below right)
- Vanessa Hudgens & Zac Efron (similar to the Timberlake/Biel case, Hudgens isn't fully okay with the situation while Efron doesn't actually want Hudgens to date around)
- Pink & husband Carey Hart (tried the open relationship thing back in 2007 but no longer seem to be "open")
As you can tell from the varying details of each couple, the "open relationship" thing can become fairly complicated. I'm going to try to categorize the eight couples into the different ways they seem to think of open relationships.
One-sided openness: Mo'Nique/Hicks and Fox/Green. Both of these couples seem to have agreed to being open but only for one partner. Interestingly, in the former, the man strays, while the woman strays in the latter.
Mutual openness: Smith/Smith and Swinton/Byrne. Both of these couples seem to have agreed that it's okay for both partners to have relationships outside the marriage. However, in Smith/Smith, it sounds like either partner can have sexual relations with whomever they want (with approval) but the emotional commitment is to the marriage. With Swinton/Byrne, although they are married to each other, they only have one outside-of-marriage partner. Thus, they are faithful to their spouse and to their partner and do not have any other similar relations.
Open in theory but not in practice: Jolie/Pitt. In this couple, although one partner is okay with polyamory, the other is not, so the couple's stance "rounds" to monogamy.
Not really open: Timberlake/Biel, Hudgens/Efron, and Pink/Hart. These three couples don't really sound like they were being happily open to me. Timberlake/Biel and Hudgens/Efron both sound like couples in which one partner is ready to settle down while the other one isn't quite ready yet, so the more-serious partner throws out the "open" label to keep the other partner happy while waiting for him/her to settle into monogamy. Pink/Hart sounds like the couple that was having issues, so they tried the open-relationship thing to try to "save" the relationship/marriage. However, since they actually prefer monogamy, the polyamory thing did not work at all (and never would have), so they have returned to a closed relationship.
The first two categories I came up with, I think, are actual successful open relationships because both partners are cool with the situation. Of course, the details differ greatly (only one partner being open, full disclosure and consent of extramarital affairs, being "open" to only one extramarital partner).
So polyamory is not for everyone. Both (or more) partners in the relationship need to be happy and aware of the constraints. It's all about communication.