A great article from Jared Spool on gaining insight on user behaviour from your search logs. This is all about how visitors use your site search, rather than the terms they type into external search engines to access your site.
The section "What Are the Top Terms for Pages on Your Critical ClickPaths?" is particularly pertinent to content driven websites. What terms are visitors searching for when they depart content pages? This is the point where they give up reading or navigating and these terms give insight into their expectations from the page or section.
Spending Quality Time with Your Search Log -article by Jared Spool