I really like where you are going with the group matrix thing. It actually is ideal for me in that I run a social network of polyamorous people. The ability for profiles to join as part of a unique identity but also retain their individual profiles is outstanding for a number of reasons, not the least of which is that if there is a falling out between any two people, they can withdraw from the group and still retain their individual profile and adjust the status.

As far as the couples thing, see more are you talking about a mode that only joins two distinct profiles? The only thing I would say is that if they are both equal admins, you would best find a way to handle eventual "divorces". I could see disbanding getting messy if you set it up like the groups idea. An existing couple living together will typically sign up under a couples profile. For the sake of argument, let's call the adjoining of two profiles outside of the existing couples profile setup a "domestic partnership". The simplest way to handle "domestic partnerships" is to allow them to exist as a network and not under the same parameters of a group where you have group photos, forums. Let them keep their proprietary profiles, photos, and friends but let there be a feature where someone can see who they are coupled up with. Then someone can decide if they want to befriend the individual or the couple. If both accept, then from that point on, they show up as the couple on the person's friend's list and any communications are sent to both people.

I think "coupling" and "uncoupling" would be a rather unique feature that is a step above the everyday friends list. I could see people sending out invitations to couple with someone and an option to dispatch an email announcement to all on each person's friends list. It should also keep a history of how long they have been coupled and with whom. When people "uncouple" it would be a lark to send out an automated breakup notice to those who were friends with the couple.This would be quite telling after several breakups but I think it would really gain notoriety as a feature and I would make it only removable only by the admin.

Outside of the novelty, I think it would be interesting to make online relationship histories as public as everyday relationships. Some Casanova secretly sweet talking too many at one time would certainly get pressure to "couple" up and get slammed. But then the option to turn off that feature in the control panel has to be there for webmasters for whom it would be a deal breaker. Overall, I think it would be a hit. Just a thought.