I think Danny Sullivan first described search as a “reverse broadcast system”. It’s a great way to describe the value of search, and how to approach search in terms of marketing.
I liken search engines to being a ‘reverse broadcast network.’ People pay tons to be on television because you can get your message out in front of millions of people: broadcasting. With search engines, millions of people are telling you *their* messages: what they want to buy, purchase or get information about. You don’t broadcast to them; instead, it’s the reverse, they broadcast to you. There’s very little if anything as a marketing or information medium that I can think of that compares to this. It’s golden and still today amazingly unrecognized.
In search marketing, you prosper when you let your visitors determine your content. They broadcast their intent to you, by phrasing a search query, so you should listen to that intent, and respond by providing appropriate content. Google does the match-making.