Actually there isn't a UI really to App.net per se, its an infrastructure play, more twilio than twitter. They built a UI for demo purposes to let people know that it wasn't vapor. They don't even refer to the UI as app.net, its called Alpha to differentiate it. App.net is the apis on git hub, some of which are baked, enough to build Alpha. If you get a dev subscription you get api keys. Ive seen some pretty cool stuff already. The idea is that you build whatever social experience you want for your product. here is a for instance. Suppose you are the new york times, you could build social into your website and apps. subscribers could then see their social interactions and data in context rather than crammed between a cat photo and a belly fat ad on or underneath an unrelated tweet. Sane people could go have a convo and exclude trolls by forming ad hoc groups etc... tailor to the audience and the site to enhance the experience.

Also, there are/were cool people in Alpha and it wasn't so crowded a few hours ago that you couldn't talk to them. Famous VCs, internet celebs like Gruber and McCracken and Siracusa, regular celebs like Stephen Fry etc... I don't know what the plan is for Alpha but the point is the infrastructure not Dalton making an ad free twitterbook clone. Other people have already made better UIs than Alpha even. Apis pretty easy to use.