you will notice a welcome message by Google that states
Regardless of how you drive traffic to your site - paid search, search engine optimization (SEO), print, or any other medium - your challenge is to get more of the visitors you really want for the lowest cost possible. This section of Conversion University focuses on marketing optimization: how to target your marketing and get the most out of your spend.
Clearly, Google acknowledges that SEO is a valid way of gaining traffic to one's site. How many of the SEO techniques out there do you think Google actually endorses?