Family Contact List
Our family base set of contacts we all care about, such as our core family and friends. It would be super helpful if we could have a family contact list much in the same way Outlook.com provides the family calendar feature. That way we can all share/manage that core list. As it is now my wife and I have to manage our contact lists separately, which creates a lot of unnecessary work. I can share a contact, but that is a "point-in-time" share. If one of us makes updates to that contact again, the other does not receive the change. People are important to us, and our contact list represents the most important people in our lives. This is the single most useful feature you could add to Outlook.com.
This is a common problem that also applies to small groups and organisations. But it can't be done in this technology as far as I can see. You haven't got any shared server version of a list. People lists aren't even kept in step with contact changes eg changed email addresses, they are just a copied snapshot, so outlook is worse than many alternatives in this area. But none of the popular email programs seem to offer a shared list facility such as you would like.