A lesson learned from app.net is that when all conversations on a social network are meta-conversations *about that social network* you get an incredibly boring, self-centered echo chamber that's very unappealing to most audiences (which, in turn, makes it more boring and self-centered).

Disclaimer: not *all* conversations on app.net were about app.net. Far from it, actually. Still, it was such a prevalent topic that it might as well have been the only one. I'm convinced this is what killed it.