I keep coming back to this article. Here's my favorite part:

Facebook has utterly dominated the definition of the social graph to the point that conventional wisdom in Silicon Valley says that they have already won social.

Few analysts seem to notice that the particular definition of "social graph" promulgated by Facebook -- people you already know in real life -- is not the only possible social graph. In fact, Facebook's future revenue will actually be built on top of another social graph: the social interest graph, aka Pages and Likes.

Twitter's social interest graph is potentially a huge cash machine that will lift the company out of the red and into the black . . . (Naval certainly hopes so).

An interest graph differs from the "people you know in real life" social graph in that it is:

• Built on one-way following rather than two-way friending

• Organized around shared interests, not personal relationships

• Public by default, not private by default

• Aspirational: not who you were in the past or even who you are, but who you want to be

It should already be clear that the interest graph lends itself brilliantly to commerce.

For more, read the full article.