Number One: Facebook is not a social network – it is a facilitator of social networking, an important distinction.
Number Two: To understand Facebook best – and therefore how to use it – think about where it came from and what it was designed to do, its optimum state. It grew out of a single university campus and was designed to link together relatively small groups of people all of whom had something very specific in common and who probably actually knew and met with each other in the real world. All this other stuff – Robert Scoble and many others of the digiratti with their thousands of friends, the pages, the applications, the commercial involvement – is largely pulling it away from its optimum state and creating tensions that will probably become critical in the near future – unless it does some fundamental re-structuring, along the lines below.
Number Three: If Facebook wishes to remain successful it needs to build from its optimum state – and focus on helping people find and connect with others around areas of shared interest, forming small genuine social networks hosted within the Facebook infrastructure. Note, Facebook Groups is a long way short of this – but may indicate the direction to head. Lessons here can be learnt from Ning and also from My Space – given that much of the success of My Space came from the ability to create networks around music and bands.
Number Four: Facebook’s greatest contribution to the history of social media will probably lie in the fact that it brought the mainstream into the game. It will have given a large number of people experience in creating and managing a digital identity, uploading content and interacting with other people on-line.
Conclusion – because Facebook isn’t showing any signs of focusing in the direction outlined in thought number three – I would give it 18 more months as the king of the hill, 18 months after that as still in the game and then it will be sold-off as a membership list (for considerably less than its current valuation) to someone with better ideas.