Ash I think Marco summarised the problems perfectly on ATP recently, while discussing Ello (atp.fm/episodes/86 @ 11:20). The perfect solution is (maybe) a decentralised protocol that can be either self hosted, or operated as an "island" (think Gmail and Hotmail to email), ensuring accessibility to a wide range of people. It's a difficult problem, and decentralised efforts have been pretty unsuccessful in gaining traction so far, but to me this is the holy grail (a decentralised, popular system that is accessible, easy to use and miraculously becomes as culturally relevant and widely used as Twitter).