This is the first story I've heard in months on this website. Who's using it? Has anything meaningful happened behind its paywall? Is there anything at all besides a gimped Facebook clone or whatever the hell it is?
It isn't just a "gimped facebook clone", the App.net service is a framework for developers to build a multitude of social networks on top of a single platform. The microblogging aspect was just the easiest "get" for them out of the gate. You can look at their One Year post [0] if you want to see a list of everything that they've implemented.
[0]: http://blog.app.net/2013/08/14/we-are-just-getting-started/