Our research in internet sites shows designers should generally avoid relying on Search to help users. Search's track record is, unfortunately, very poor and usually fails far more often than it succeeds.
On intranets, the pull to use Search is stronger, since it promises an easy way to drive users directly to their content. However, our research shows that users only resort to Search when they can't find the trigger words on the page. They turn to Search, typing in a query representing the scent they had hoped to find -- in essence creating their own links.
Search logs are a great way to identify what scent is missing from your portal. When going through the logs, you want to look at both the queries and the pages from which those queries originated. The scent is telling you where the scent is lost and what link the user desired.
In a recent analysis of one of our client's search logs, we discovered that 84% of the searches were for contact information on other employees. Only 16% of searches were for non-people-related content. A quick implementation of a "people finder" dramatically reduced employee frustration with the intranet and increased overall satisfaction.