Social currency can be described as "the entirety of actual and potential resources which arise from the presence in social networks and communities, may they be digital or offline". The mere presence within these networks and communities - and just spamming content - is, however, not enough.
On our own your or I are worth nothing - we are just individual islands in the social ocean, cut off from everything around us. Where our paths cross is a different matter; those intersections, the relationships between us, are the interesting bits. The relationships we form provide the true currency that we can trade on the social web. This currency can be employed by individuals, service providers and others - such as advertisers - alike.
For us, the consumer, social media is a dead experience without friends or followers - the clue is in the name "social". We must interact to garner any benefit from the service. Service providers need users creating relationships for the site to function as intended - an empty site is bad for business. Often user demand drives the path the service will follow especially with regards to functionality.
Advertisers sit above all of this looking down with a holistic view. Without any form of relationship it is hard to target ads effectively. While a good deal of information can be gathered by anonymous browsing statistics they only show isolated areas: 1000 people visited this page, 2000 that page etc. you do not have the relationships. They want to be able to see the links, e.g. who visited both to establish a better profile.
Look at Amazon for example. For years we have seen the "people who bought x also bought y" information below the products we are looking at. If you have a known connection between two or more products then it makes sense to bundle them for a reduced price and hopefully make additional sales.
We need the patterns and the relationships to go one stage further; patterns of traffic, of use, of interest and of 'likes'.
There's the key word: likes.
Now we can see why Facebook wants to link the web together. Why else would they be willing to undertake this herculean task?
They don't want to control the web, they're not a content creator and don't want to absorb the content of others - they want to provide a means to join the dots, find the patterns and, by doing this, leverage our relationships (with each other, with sites, with Facebook themselves). Should we be so surprised?
Image by juhansonin