I was going with the example of Facebook using their knowledge my tastes, as well as the tastes of millions of people who are somewhat like me, to introduce me to things that I would have a legitimate interest in, even if I'm not searching for them.

Example: Subject is a coffee-drinking, Vespa-riding, snappy-dressing, backyard chicken-farming, photo-snapping, game-playing father of two small children. He's not looking for bluetooth cuff links, but we know that once he sees them, he'll be likely to buy because that's what other people in his micro-niche tend to buy.