Think about this: By reading this blog, you and I are connected. We have this blog and its topics in common, so there's a chance we have other things in common as well. In any relationship there is a degree of trust and influence. If you trust me, at least in terms of particular subjects, then I have some influence over you. If I buy an iPad, then there's an opportunity for me to influence your possible purchase of an over-hyped tablet that you don't really need.
So what could a retailer do with this? Retailers that have fans and followers should assume that the friends of those fans and followers are more susceptible to their marketing efforts. If I'm a fan of Apple, then Apple will be more successful marketing to my friends than marketing to random people. Intuitively that makes sense, at least to me. Companies like 33Across and Pursway are already putting this theory into practice, and achieving some interesting results.
Jeff Jarvis, who by-the-way is speaking at CrossTalk this year, has been discussing the power of influencers in social networks. In his blog he rails against marketers and says "messages and influence aren't the future of marketing; conversations and relationships are." Valuable messages will be passed on because they are valuable, not because someone has the power to exert influence.
True enough, but that won't stop the efforts underway to leverage social networks for more targeted advertising. From a business perspective, this sounds like a goldmine to me; on a personal level, it's a bit creepy.