One of the things discussed at length in The Four Hour Work Week is the idea of using Google's AdWords as a tool for testing consumer behavior.  I have some experience using Adwords.   In the last year I developed two e-Commerce sites, www.busbeetruckparts.com and www.tylerbrothers.net, both of which have had some success brining in quality traffic through the use of Google AdWords. 
Additionally, I've done a bit of research and had some success using keywords and metatags to gain naturally high rankings, particularly for the Busbee site. 
I'm also a Drupal developer (Note:  this site is being developed with Drupal 6.1)  and I try to stay apprised of any new Drupal sites being developed.   Today I found a site called www.seobook.com, a Drupal-based site that includes a blog, a discussion board, and a number of lessons and tools for improving one's SEO skills.  It offers a personal SEO coach for $100/mo.  Here's an interview with the owner of the site: http://knaddison.com/drupal/interview-with-aaron-wall-seobook-com-about-migrating-drupal-and-seo-0