The Changing World of SEO
Leave it to Aaron Wall at SEObook to continue to provide innovative perspectives and high-level content on the nature of SEO. Here he provides a large graphic on How the SEO Industry Went Corporate which not only outlines a relative history of SEO and search marketing but also points to the future. (You may need to click on the graphic again, after it appears, so that it can be enlarged further).
You can also access the graphic via the original blog titled, Corporate SEO Services.