Oh snap you got me, I never thought of that. But wait we weren't talking about search were we? No... Also the methods for upstream sales; in particular with Google are passive and common knowledge.

You are right. But Google isn't a social network; neither is Priceline. Auctioning users of a community, and auctioning users of a tool or service are two different things. There is no expectation of trust, except for privacy, when using web services such as Google, or Priceline. Whereas a user in a "web community" gains trust in a particular site. If the site uses that trust for gain, without being completely open about it then its akin to forced spam.