I've just started playing with Path, a new network developed by some Facebook alums, Shawn Fanning and others and backed by some pretty amazing VCs.
At first glance it feels a lot like instagram, with easy sharing of photos that can tagged with people, places and things. But what makes it interesting is the in built ceiling of 50 friends - it means it becomes a personal network for real friends where you can share much more meaningful stuff. And it means as the user, you'll be a lot more choosy about who you want to be your friend. Be interesting to see how the content and behavior adapts as a result.