Facebook has too much central control.
Social networking should be based on a decentralized system of independent nodes such that no single authority owns the whole damn thing and makes everyone obey their rules, and has everyone's personal info. (And all protocols documented, and implementations open-sourced, needless to say).
Again, a social network only needs to know whom to send your message to and need not know about the contents of the message, If USPS opened our letters, would we argue for a decentralized architecture where we individuals ourselves drove around delivering letters in our spare time?
How were so many of us tricked into handing over so much control?
I am curious to know what you're basing this statement on --"Fast" and "efficient" are not necessarily related.
(For instance, there seems to have been an explosion of decentralized message-queueing mechanisms available for coordinating distributed software systems. A centralized system can suffer from efficiency issues as easily as a decentralized one.)
This means the storage location of the messages you are supposed to receive could change often, making retrieving messages a two step process, looking up the current online location and then retrieving messages. The place to lookup messages is fixed in a centralized system, hence you'll receive messages faster.
This can definitely be sped up by increasing the number of times the messages are replicated in the decentralized system and a constant shuffling of the message between nodes to ensure it is always available for the receiver when they come online, hence inefficient.