Relegate Booleans to Advanced Search Boolean search should be avoided since all experience shows that users cannot use it correctly. Almost all users will enter the query cats AND dogs . In our studies, they typically do not find anything, since the site does not include pages that mention both animals. Unfortunately, most users have not been taught debugging, so they are very poor at query reformulation . This is why I recommend minimal use of scoped search and no use of boolean search in the primary search interface.
Advanced search is fine if offered on a different page than the simple search.
Search is one of the few cases where I do recommend shaping the user's behavior by intimidation. For example, if the site has a FAQ about a query term, then the FAQ page should be listed on the top of the results page even if other pages have higher relevance scores. Also, hits on a series of pages that belong to the same area of the site should be collapsed into a single reference to that subsite. On a final note, elementary schools should start teaching search skills. The future of user interfaces is almost certainly going to be dominated by various ways of searching immense information bases and gradually refining the retrieved set.