I still disagree, I think we've just seen the beginning of what social networks will do in this century. Facebook is barely scratching the surface, and there is ample room for disruption. It is inevitable that new ideas will emerge, and they will be embraced.
You are moving the goal posts here quite a bit. Do I think that facebook will forever be a giant, without question? Of course not. What I disagree with is that all it takes is a good idea.
I believe that the more likely course of action, as others have stated, is facebook will make mistakes which will be capitalized upon. Large organizations gain cruft, slow down, choose the wrong direction. Many things can happen.
