SEO is something you do to your website. It isn’t a marketing plan. Companies that live off of SEO optimization for lead generation are living on borrowed time.
At some point…and it always does, the search engines will take away whatever favor they’ve shown your site and you will then be faced with the dilemma of building traffic to your site again.
Use SEO, make it part of your site structure, just don’t count on it as a business driver.