SEO success - traditionally measured by target keyword rankings and traffic - should be measured by ROI instead, according to a presentation given at eMetrics San Jose 2009.

Below, some highlights (via Search Engine Land).

• Rather than rankings and traffic, focus on conversions - that is, impact on revenue - as measures of success.
• Calculate the ROI of our organic traffic as you would do for all other medium. Free organic traffic is possible, but investments are needed to attract masses and make changes to website, so you should invest resources, either with an agency or in-house people. Taking all the expenditure into account will give you an idea of how much profit you are getting from your organic traffic.
• Keep in mind the possible downfalls of making your site focused on conversions. An often repeated truism in SEO circles is that content is all important when it comes to SEO. Yet there is a trade-off between content and usability or design; you should neglect neither. Including more content on the page should not hurt the conversions of the website.
• Choose carefully and optimize SEO landing pages. Landing page optimization is as important in paid search campaigns as in organic SEO campaigns; both should be highly efficient in converting incoming traffic. A useful tool to test the success of SEO landing pages before you target them is AdWords.
• Optimize the snippet that appears on the search results page. This is the user's first interaction with your website, and ultimately may determine the click through rate from visitors coming from search engines.
• Use internal search to expand your keyword targeting on search engines and to give customers what they are looking for. Optimizing SEO by measuring the success of keywords bringing traffic to the website is great, but by doing that you lose a precious source of keywords your customers are typing in your website, i.e. your internal site search. This is what they are really looking for, and you should check if you are targeting those keywords.

See all slides from this presentation.

Last year a study found that the presence of display advertising significantly affects click-through and search style across both paid and organic searches.

In 2007, Google-sponsored eye-tracking research found a significant correlation between brands appearing in the top organic search and sponsored placements, and consumer brand affinity, recall and purchase intent.

Measurement firm Hitwise also began offering customers trend data on both organic and paid search terms in December '07.