Search marketing works because it understands search's essential nature: people looking for stuff. Where social networking advertising (at least the passive model that uses banners or, in many cases, contextual advertising) falls down is it fails to recognize the essential nature of social networking. People come to hang out with other people. Anything that gets in the way ruins the experience and will be avoided.

This is why widgets have been getting so much play lately: they don't intrude on the user experience. Yeah, they're branded. Yeah, they're obviously a product of crass commercialism, but when done well they enhance rather than detract from the experience. They're something to share within a social network, not something to detract you from it. They can become part of the conversation you're having with friends and acquaintances, not an interruption of that conversation.

In a survey this year, Yahoo Travel found that 61 percent of people now go online for vacation recommendations, says Fiona Lake Waslander, the company’s director of product management. “Travel 1.0, when travel planning moved online, was really all about prices,” Waslander says. “No longer are you looking for a hotel just based on a price, but you’re looking at user reviews and user ratings and photos.”