Fascinating read by David Segal.
New York Times: Search Optimization and Its Dirty Little Secrets
If you own a Web site, for instance, about Chinese cooking, your site’s Google ranking will improve as other sites link to it. The more links to your site, especially those from other Chinese cooking-related sites, the higher your ranking. In a way, what Google is measuring is your site’s popularity by polling the best-informed online fans of Chinese cooking and counting their links to your site as votes of approval.