Early adopters aren't tired yet because App.net's continually releasing interesting updates to the platform. And there's even a great example of 3rd party developers working together on their system to extend and support one 3rd party developer's chat system (patter). So each developer's project help retainer interest as well.

So as long as App.net keeps releasing new APIs and developers stay interested in the platform. I don't think early adopters will get tired.