Maybe interesting,

"Well, you can't specifically track the exact position of the keyword that was clicked like you can do with AdWords. But it is possible to determine the page he was on. A ranking tool can tell you over and over again that a certain keyword is around position 15 in Google while Google Analytics claims he is on page 1 (position 1 to 10). This effect can come from 'personalized search' or 'local results' that can influence the Google rankings dramatically. People see other results than you see with your ranking tools. And therefore you need Google Analytics to do the real ranking. "

http://yoast.com/track-seo-rankings-google-analytics/

I've seen that in April on a French blog:
http://www.wagablog.com/2008/04/sur-quelles-pages-de-resultats-de-recherche-vos-visiteurs-vous-trouvent-ils/48

you can also track search engines robots while they are tracking your website:
http://www.remiaubert.com/post/maitrisez-votre-seo-referencement-naturel-grace-a-google-analytics/ (in French too)