I don't need another social network. I don't need ads removed from my current social feed. I don't need app.net.
If twitter died tomorrow something else would pop up. That's the nature of the space. We don't need it and so we go where there is less friction. Ease of use, ease of joining, and ease of finding those I care about most. That's all that matters.
I see App.net becoming something much like svbtle. A highly curated space much like a country club where only those willing to pay the entry fee are allowed in.
Cool.
As long as the data is available publicly through feeds and other api's it won't matter too much. It's still blogging, it's still tweeting, but now your participants have been restricted. Not as much as Svbtle but enough to encourage a certain atmosphere.