There is a fresh thread at WebmasterWorld named Google algo moves away from links, towards traffic patterns. This reinforces what many have been saying for the past year or so. Google's popularity came from using linkage data and PageRank to score how popular a Web page is. Times are changing and algorithms need to shift. Linkage data, although incredibility important, is not the complete future of Web page popularity. Traffic is where the popularity is heading, and Google is trying to lead the pack to it.
How does Google measure traffic of a Web site? They can look at dozens of factors, including clicks from the SERPs to your page, and then back. They can use the Google Toolbar data, AdSense data, AdWords data, Analytics (although they would never), and so on. Just keep thinking....
Forum discussion at WebmasterWorld.